Any reason not to vent the radiators into the wheel wells (said by Pelican to reduce

[Edit: the title got cut off - it should say "... (said by Pelican to reduce drag and lift)"] While the air passing through our radiators is vented down, on 997s, 987s, and 996 GT2s and possibly others, it's vents into the wheel wells. Pelican Parts have an article showing how to get a very similar set up on our cars, and say it cools the brakes and reduces lift and drag. And no, this does not seem to promote the sale of anything in particular: http://www.pelicanparts.com/techarti...ell_Liners.htm I first heard of this from a post by The Radium King, here: https://rennlist.com/forums/996-foru...nd-997s-2.html He added further info suggesting the lift and drag benefits are real. But … is it really so simple? While the stock system of venting air down doesn’t seem like a great idea, everything I’ve ever heard suggests you want to get air out of the wheel wells to reduce lift and drag, not into them. That, after all, is why the 991 GT3RS’s wheel well vents are such a huge aero win. And on our cars, the air from the radiators is actually sent out down and towards the outside, not just down, and there is a small spoiler in front of the wheel wells that at least partly deflects that air from entering the wheel wells. Clearly Porsche thinks it’s a good idea on 9X7s and some other cars. But could it not be that they do this solely for brake cooling? (It occurs to me that all of these cars were available with PCCBs. I’ve no idea if they need more cooling, though I understand PCCBs on 996 Turbos are quickly destroyed on track, whereas 997 PCCBs are not.) Can anyone help substantiate / confirm / deny the drag and/or lift benefits? And does anyone know of any other reason not to do this? Thanks!

Great thread IMO. I have though about the same thing because once while the speedometer was hitting triple digits and having the gas tank some what near empty. I could feel the front end of the 996 get squirmy. Yes tire pressure was to specification, tires were properly balanced blah, blah it could be a lot of items but I am open to the front aerodynamics being better vented instead of it feeling like it's generating lift. Like in one of your links in which it demonstrated how to cutting fins. I though about doing something similar but instead of cutting individual fins. I was going to buy a ready made vent that only need a 4" cut and then can be secured via popfasteners or just snap in place for a nice clean more streamlined look to the mod of venting air out.

I've wondered about this too. I've removed the condensers and fans from my track but have left the ducting that vents the air down. At 142mph on an 8 degree bank it was plenty stable but I also have front and rear aero to assist.

Where is the wind tunnel telemetry showing lift and drag are reduced by this modification?

Quotes source post: 13848230

+1 internets Aero is complicated. Changing one thing changes others and without wind tunnel experiments/data it's guesswork.

You can accomplish similar results with a decent data acq system by analyzing speed, g's, and slip. If it had a positive effect it's good, and a negative effect its bad. Not near as scientific as a wind tunnel but a whole lot cheaper. Have you seen the rear wheel wells on the Cup cars? It was surprising to me. Attachment 1121405

Quotes source post: 13848283

Invalid Attachment

photo261.jpg Any better?

Much

Quotes source post: 13848283

I'm thinking no, the goal of aero on vehicles is not one just for speed. So without wind tunnel testing, you are not going to be able to quantify anything.

i think the benefits would be most apparent with entry speed at turn in. with less lift at the front you should be able to brake later and enter faster. all things being equal (tires, suspension setup) a consistant driver should be able to see an improvement in average lap time. folks talk about overall balance of the car, wind tunnel testing, etc., but as most armchair drivers state, unless you are on the autobahn it isn't going to matter. i agree. i really don't care if my car flutters off like a leaf at 300 kph, because i will never be going that fast. i care about entering corners faster and getting the power down sooner on exit. if i can get more downforce/reduce lift on the front then i'll take it. if the rear now feels lighter (it most likely won't be, but it will FEEL lighter due to the heaver front) i will take it - i can steer out of oversteer but have to lift to correct understeer - slower. further, i can rebalance the car with swaybar adjustments, different brake pad compounds, tire width, etc. - i don't think it is faster to compromise one end of the car in order to balance with the other.

Ok I'm confused. I know nothing about aerodynamics, but I do know on my 2005 C4S that there are louvers behind my radiators that dump into my wheel wells!!??

yup. on the 986 and 996 they dumped the air from the rads under the car instead. porsche is constantly improving their designs (ims anyone) based on failure rates, racing innovation, planned obsolescence, etc. this thread is about trying to incorporate 997 radiator venting into a 996. really, if a person has an early 9x6, there's lots of stuff to be stolen from later 996 and 997 porsche design and improvement. and you would think that you should have the confidence that, if it made sense for porsche to either change or add to their track cars, then it should be good enough for you. turbo rear brake ducts? oil piston update? gt3 front brake ducts? tensioner and tensioner pad update? 4-channel abs? third radiators? third radiator venting? 997 oil cooler? just do a quick tour though the parts catalog and look for superceded part numbers and ask your self why.

"yup. on the 986 and 996 they dumped the air from the rads under the car instead." My point is my car is a 2005 C4S 996!

Got a different question relating to this mod. I do not track my car (maybe someday since I have several great tracks within 100+ miles) but do live in a climate where it gets hot (over 100 deg) on a daily bases in the summer. I have read on other posts that hot air gets trapped behind the radiators (not sure if this is true)? If so, would venting into wheel wells help with air flow through radiators and cooling of the engine?

i think the turbos got vented fender liners as well, with the gt2 (introduced mid-way through the 996 model run). if you have a c4s you got turbo bodywork.

Quotes source post: 13848941

If the air got trapped the engine coolant temperature would rise even in less than 100F temps. The air doesn't get trapped. It flows through radiator duct and condenser and radiator and exits where ever the exit is, under the just ahead of the front wheel well, or perhaps into the wheel well. I've driven my 2002 Boxster with its less than optimum aerodynamics and with its radiator air exits just ahead of the front wheel wells and in 116F temps and in triple digit temps many times. While the coolant temperatue gets up to 226F it doesn't get any hotter than that.

Thanks for the response Macster

Quotes source post: 13848569

I'm thinking yes, but ... Wind tunnels can't be beat for design work. You can't hold smoke generators in front of a car going 150. And you couldn't see very well where the smoke was going over, under, around and through the car even if you could. But no matter how much time you spend in a wind tunnel, you never know for sure how well the aero will work until you drive the car. For this and other reasons, final aero adjustments on racecars are made at the track. On the other hand, the aero setup that minimizes laptimes might not be the best for street cars, where higher priority is usually given to fuel economy and top speed that to downforce. I certaintly don't want all the downforce I could get if I chose a GT2 bumper, wing, and lip spoiler, even if I do want more than I have. However, while sending the Stig out on track to tweak the aero is not the right way for a street car, a good driver can confirm whather an aero mod produces significantly less lift in the front, rear, or both, as well as whether it leaves the car well balanced. Though regarding balance, what feels right on a typical track with speeds reached there might feel quite nervous at 177 mph. So while I'd love to see wind tunnel data, I'm in principle willing to make aero mods without it. On the other hand, I'd be a lot more confortable if 10 drivers say "I've tried in on track, I've tried it on the autobahn, I'm a professional race driver, etc." than if just one driver whom I don't know says I tried it and it works. And so far, I don't think I've seen anyone say even that. Surely someone on the forum has done this mod?

Quotes source post: 13848817

I'm a bit confused by the question marks at the end of the sentence. Does your 996 C4S definitely vent to the wheel wells? If so, that seems like further reason to be comfortable with trying this on a Carrera. However, it could be that this works with the very similar C4S, Turbo, and GT2 front bumpers (where for some of the incoming air, the downward path would otherwise be even longer), but not on Carreras. Anyone know how the air is vented on a 40AE? I can't remember, did someone say Porsche did this on one (or more) of the 996 GT3 variants? Or just that some owners of GT3 race cars did?

Quotes source post: 13848913

I know this is a bit off topic, but what are these about? Perhaps the first is an improvement which was introduced with the 996.2? Or ... ?

You are missing the point. If you are able to take a high speed corner on a race track at 90 mph with 1.4g's and a 7 degree slip angle prior to the aero change and you are able to take it at 92 mph with 1.4g's and a 5 degree slip angle afterwards then you know it had a positive effect. This is easily calculated with most club level data systems. I have my doubts as to whether it would achieve a measurable difference but if it did you would be able to log it. The other place you would see a difference is if you had a heat soak issue and it seemed to improve with this modification. But the stock brakes are amazingly good on the C2 and I have yet to see this as a problem that needs fixing.

Quotes source post: 13849084

Yes it does definitely vent to the wheel wells. TRK seemed to be indicating that 996's did not have radiators vented into the wheel wells. I was simply pointing out that some do indeed have that arrangement. He is correct that the C4S does have the turbo front bumper/ radiator air ducting. The front end on these cars are different and, therefore, I have no clue what impact a modification to a C2 would have on performance- cooling or downforce. As has been said many times..."May the force be with you..."(my apologies!)

As has been said, aero is tricky. Also, after testing in a wind tunnel where everything is controlled then the car is tested and tweaked on the track. Cool real story from decades ago at Nascar: at one race, Petty lost his rear bumper during the race and noticed a significant speed improvement. Of course, Nascar wouldn't let him remove it from the car, so for the next couple races they would bolt the bumper on with a couple of soft brass bolts, and he would get accidentally 'bumped' so the bumper would fall off. Once off, they did not have to replace it, and he would get a nice speed bump. Tricky..... Fairly low tech way to test a reduction in drag, but not downforce is to get a sensitive manifold pressure gauge like found in many aircraft. Do a test run and carefully note rpm, and manifold pressure(which can be easily translated into HP) during a baseline run. Make your mod, don't change anything else like add fuel, change tire pressure, etc and then make another test run matching rpm, and note any change in MP. A higher value in inches of Hg will indicate a less open throttle plate, and a reduction in torque and HP required under the same test conditions as the baseline test. The downside to this test is that many aero mods don't have a marked improvement until the car is moving fairly fast(since drag increases at the square of speed), so quite often the throttle plate will be nearly full open. Lower gear is best to reduce MP while keeping the rpm high as possible. So, if you can do the speed in fifth gear and also in sixth gear, it would be better in fifth to check MP delta. This is not an exact method, but I've used it before on street stock cars when designing the cooling ducts and belly pans. You need a sensitive MP gauge, and a digital unit would be ideal.

Quotes source post: 13849265

Thanks for confirming that. Does your car also have the ducts that hang down in front of the wheel wells, where the air from the radiators is vented from a normal Carrera, or did Porsche close them up?

Quotes source post: 13849530

There are also ways to measure lift and downforce. Google will turn up a few. And I've been thinking about one which might work well with our cars. 996s with Xenon headlights have ride height sensors. Definitely at the front axle, probably at the back too. If one could tap into the data coming from these sensors, one could both determine how much lift one is getting front and rear, and also how different modifications affect that. And at least on some cars, it is possible to tap into the data. Here’s a link where someone did it with a Lexus: http://www.autospeed.com/cms/article.html?&A=113225 There is a simple way to translate changes in ride height into kg of lift or downforce. Put some weight between the wheels on one axle (e.g. in the frunk or behind the rear seats) and measure how much the height changes. This tells you how many kg are needed to move the height by X mm, so if you know the car rises Y mm at speed, you can calculate how much lift you are generating. I believe there are also easier ways to test for an increase or decrease in drag from some aero change. The simplest, but not easiest to do, is seeing if it impacts vmax. One can also test changes in acceleration in 6th, e.g. from 90 to 110. Or changes in coast down time between similar speeds. (Though with the manifold pressure method, it may be easier to quantify the change in drag in terms of hp equivalent, or even the change in CdA.) Anyway, it would be great if someone could figure out how to tap into, read, and save the ride height data. If so, I’d happily do this wheelwell mod, test it at Autobahn speeds, and report back in. I'd probably test another mod or two as well.

Quotes source post: 13849827

Car not in air but there does appear to be an opening directly behind the rad fan in front of wheel wells to the bottom of the bumper cover. I do know when fans are running the best place to check for air flow is at the center of the leading edge of the front fender well coming from the louvers in the well. Another thing of interest is on the parts list the 4S and the anniversary edition show four "air flaps" at the back of the fan air box. There are no similar listings for C2's. (?) I think this discussion is above my pay grade!

hey rs10, you appear to be a technically-minded fellow, so here is a link ... http://www.autoatlanta.com/porsche-p...section=801-75 this is the porsche online parts diagrams, provided by auto atlanta so that there is a price, and sometimes an image, tied to each item. i've no affiliation, but find it a readily-available source of parts info (and one of the places i stop when i am price-checking between sunset, suncoast, pelican, the local dealer, etc.). the particular page i am pointing you to is the 911-996-gt3-body-fender liners diagram. if you look at fender liners for the gt3 you'll see that they change mid-way through the model run. if you search the parts numbers, you will find images of each - the early ones are not vented, the later ones are. this was done with no significant change to the front bumper cover/aero (ie, the 996 gt3/aerokit unit). a similar search of other cars will show venting for the turbo, c4s, AE, and all 9x7 cars. you asked about tensioners, tensioner pads, and oil pistons. you can find all these parts on the parts diagrams, and all have been updated. the m96 has an issue with chain slap on start-up. as an overhead cam engine, the crank is tied to the cams with three or five chains. these chains are held in place with metal tensioner ramps. the ramps are protected from the chains by plastic tensioner pads. the pads/ramps are pressed tight against the chains by chain tensioners and variocam actuators (depending on which chain we are talking about). when the m96 starts up, due to a number of reasons (light cold-weight oil drained down, no chain tension) the chains slap against the pads until oil pressure comes up (search 'start up rattle'). check your oil filter; there will most likely brown plastic bits - pieces of your tensioner pads bashed off by slapping chains. to fix this, porsche (a) made the plastic tensioner pads harder, (b) made the tensioners stiffer, and (c) updated a piston in the oil pump (the piston is a spring-loaded mechanism in the oil pump designed to bring oil pressure up quickly; the early piston was squared at the end and said to bind - the new unit is slightly beveled). the piston is a $5 piece that takes 5 minutes with your next oil change, so whether you believe this internet wisdom or not it is easy peace of mind. the three tensioners are $150 each but can be done without opening up or dropping the engine. and the pads, well, they are a big job that can be done with the engine in, but require opening up the heads. get a durametric, track you cam deviation, and change them when things get to +/- 9 (this is the deviation that triggers a cel). and start making your 'while you are in there' list - variocam actuators (any green bits in you oil?) chains, lifters, etc.

Quotes source post: 13850151

Thanks for more very helpful info! Shame I didn't know about the tensioners and oil pisten earlier, as some work was done in that area when replacing the IMS bearing! Perhaps we did replace a tentioner or two, I'll have to look. Regarding the fenders, I googled the part number for the later GT3 part (99650412391), and while some vented images did turn up, when I was able to identify what car they are from, they turned out to be a different part, from the turbo. On the other hand, I found three photos that were apparently this later GT3 part, and none were vented. Did you find any images of a vented GT3 part? If it's just the Turbo (and all Turbos, not just later ones), then the Turbo was the first 911 (or at least first 996) with the air vented into the wheel wells, and I'm wondering why - and also why they didn't repeat this on the 996.2 Carrera. We've already discussed the idea that it works well with the bumper. On the other hand, could it be to help warm up the PCCBs? This is inconsistent with the vents being on the C4S, but that might be because they fit other parts carried over from the Turbo (e.g. the bumper). (Though PCCBs were probably an option on the GT3 MkII, no?) Or it just could be that they had better things to do than to design a new wheel well part for the 996.2 and GT3 MkII.

here's a link to a late gt3 liner: https://www.stoddard.com/99650412391.html and here is the image: you can see where the air normally vents downwards is blocked, replaced by a cutout (not vents) on the inside of the fender liner. trk out.

interesting concepts and valid observations about aero being tricky etc but there are some things that are givens and constants and fundamentals. I spent a career designing and manufacturing ( and racing ) prototypes and spent more than a little time in wind tunnels both full and scale. none of that allows me to answer this question with authority but I can shed some factual light on some of the issues raised so far... 1) in order to get flow you need a pressure differential... if the pressures are the same on both sides then the air is stagnant. if its not the same it will flow from the hi press side to the low press side. why is that important here ? simple... a rotating wheel inside a fender makes that area a hi pressure area... how hi ? don't know BUT if its higher or approaching the pressure on the exit of the rad then you aren't helping anything at all and , in fact, may be making it worse. how can you tell ? simple... pressure taps and a good data system. you put taps all over the place and map the pressures as they actually exist in the real world. I spent a lot of time venting and creating extractors for the wheel wells to get those pressures down. that's why every prototype you see has vents on the top of the front wheel arches and the rear sides of the bodywork cut back as far as the rules allow. 2) will a tunnel tell you this ? probably not unless its a VERY good rolling road tunnel and even at that , that data is static and what happens at various speeds and attitudes is often VERY much different 3) downforce and drag... maybe and maybe not but you aren't going to do something like this and " feel " some massive improvement. can you see it on the stop watch ? maybe... IF you are a professional and using a good solid repeatable engineering test regime where you establish proper base lines and sequencing and a very good high sample rate data system. . I have spent thousands and thousands of hours testing and even the smallest gains are mind numbingly difficult to accurately quantify and aero are the worst. what you are talking about here is very very subtle... not like bolting some giant honking wing on the back that makes 800 lbs of df at 30 mph or something... 4) is it real or imagined ? another good question. lets say you are a top level track guy. can run at or under the lap record all the time and win most of the races you enter... fine... so make the car stock and go do 5 laps as fast as you can on a new set of control tires. now put on a second set of new control tires and repeat. are the lap times inside of the same two tenths all 5 laps ? if so, great ... now make your aero change ( which you have pre configured ) put the original set of tires back on and do a new 5 laps . same, better or worse on the watch ? repeat with the second set of control tires... then do it all again. back to back... same fuel loads, alternating setups and tires. in the end after 50 laps or so the pattern will be crystal clear. you throw out the highs and lows and average the rest and that is your answer. sound like a lot of expensive work ? youre right... it is. but like all things you either know the truth or you are guessing. 5) can you measure down force ? sure . strain gages or shock pots. strain gages if you have push or pull rods or shock pots to measure deflection at speed. the bottom line is that all your questions have knowable and quantifiable answers if you are willing to do the work. everything else is just guesswork , voodoo and mythology. as for this specific question... from what I know and understand I can't imagine that venting the rads into the wheel wells is worth anything at all unless two things are true... one, that porshe made a pretty bad mistake about their rad exit ducting ( which I would be pretty surprised at since the EXIT ducting is twice as important as the inlet ducting ) and two that you have done something to get the air out of the wheel wells themselves in addition to all else. just packing more air in there will just make lift which is not what you want. but , again, like all things aero I could be completely wrong. aero is one of those things that you can theorize to death only to discover that , in the real world at speed, something else you never thought of actually happens.

Quotes source post: 13850660

Thank you for taking the time to offer some clear perspective on this. I for one will not worry about doing this suggested mod.

My gt3 vents to the wheels well. My old 996 didn't. I added the vents and brake scoops behind the rotors. No aero issues and cooler brakes. https://rennlist.com/forums/996-forum/495438-track-doods-brake-cooling-mod-pics.html -td

that's possible but I would ask the usual questions.... first , how do you know ? is this empirical objective data generated by instrumentation and testing or " seat of the pants " ? and I would wonder if the gt3 is configured differently from the factory both in a structural or set up sense. as an example I would start with the obvious that aero is a full concept. there are no single magic beans that suddenly transform a car. its a dozen small things to manage the pressures and flows to generate the differential pressures to make them do what you want. if the gt3 exits into the fender wells when the carerra does not then I am absolutely certain that porsche did a boatload of other small but significant things at the same time to deal with the new profile and get the air to go where they wanted and do what they wanted it to do. these are VERY smart guys and not prone to stupid mistakes. and second I would point out that aero effect is a direct and absolute function of mechanical set up. lets use something simple as example ... ride height . lets say you have a car that makes 1500 lbs of downforce at 125 mph due to an sophisticated underbody. why does that work ? because the air moves faster along the bottom surface than it does across the top surface and exploits bernuelli's principle effectively. now... what happens to that car when you lower the from ride height too much and shut off that underbody flow ? or raise it too much and destroy the effectiveness of the underbody design ? instant loss of a huge percentage of your downforce. aero is like that. even if your theory, interpretation, design and execution are all correct, the basic setup of the car in a mechanical sense has everything to do with whether or not your results will be right wrong or indifferent. I can appreciate that people love screwing around with their cars and cutting them up and changing things. that's a lot of the joy of the game but in the end there are a couple of fundamental truths that always emerge... the first is that the better you make your car for the race track, the worse you are making it for the street. for instance brakes that work brilliantly on your track days at sebring will feel numb and be ineffective when cold on the street. those track springs , bars and shocks that keep the car nice and flat on the track , make the car terrible in the wet on rt 95 going to work the rest of the time... and second... when it comes to aero it is exactly like dealing with with women... there are only two ways to understand it ... and nobody knows either of them.

Quotes source post: 13851350

Brilliant quote!

40th AE also vents the rads to the wheel wells. I've got ducted lovers in the fender liners

Quotes source post: 13850609

I found out the cutout leads to ducts or air deflectors inside the wheel well that channel air to the brakes. There's a pretty clear picture in the first post of this thread: https://rennlist.com/forums/996-gt2-...eflectors.html Someone mentioned using the 996 part on his 996 Carrera, but didn't say more. One has to wonder if this does not require additional GT3 pieces, for instance the wheel well piece in the photo above. Here are the part numbers, left and right: 99657523130 and 99657523230. Why did they do it this way on the 996.2 GT3 instead of the Turbo way? Possibly because they knew better (the MkII GT3 is the newer car). Or possibly because all they cared about on the GT3 was keeping the brakes cool, whereas on the Turbo they had different objectives. There's no mention in the thread of aero benefits, but there is of brake cooling, so if the GT3 guys understand correctly, these are designed to do that, and probably do it better than the Turbo wheelwell vents. But how this systems impacts drag and lift is unclear. Porsche may have sacrificed all for cool brakes. Still, it does seem that venting air into wheel wells on cars with bumpers like ours isn't a disaster, or else Porsche wouldn't have done it on the 996.2 GT3.

Is this for a dedicated track car? Is there a problem you are trying to solve or this just a general exercise?

So I found out how this was done here: https://rennlist.com/forums/996-foru...-mod-pics.html Well, I sort of found out. The guy who did it seems sure you can do it without a GT3 liner, but it's not clear whether he actually tried it or just used a GT3 liner ... . The other interesting note is that this interferes with full lock when he uses 245s on 8.5s, but not on the street with 8s (tire width uspecified, presumably 225). So for people running 245s on track, this can be an issue. (You may not need to turn that tight, but you may need to catch a spin ... .)

Quotes source post: 13852765

No, not at all, hence being my concern that what's ideal for a GT3 isn't ideal for me. Occasional track use, but I'm much more interested in how it works on the street. I'm looking for a way to get the front lift down to somewhere between C4S and GT3 levels with minimal drag impact, and that won't get banged up as much as a GT3/aerokit bumper would where I drive (and park). If there's a solution that reduces drag and cools the brakes, even better.

Attached is a pic of the "infamous" fender well louvers on my 4S. Question: Wondering why you are concerned about lift and drag on the street?? Your speed limits must be higher than my area! Yes, for the anti-pumpkin crowd...those are pumpkins so just call me a "loser" and be done with it!

More sauce for the goose. As the 928 was to be a 'clean sheet' design, it spent a fair amount of time in the wind tunnel. Come to find out, Hanz or Franz was having some fun and put it in backward one day then discovered that it had a better Cd going backward than forward. As the power and speed crept up with bigger engines, by the time the S4 came along, at speeds over about 145, the tail was starting to lift some. Hence the 87 and later 928s ALL came with the now infamous beer shelf back there. Not to be outdone, Lamborghini fitted a ginormous wing to the Countach in version 2 or 3(can't recall). It had the effect of slowing the car down about 6-8MPH at top end, and provided less than 30Lbs of downforce to the back of the car. Looked absolutely fabulous, was counterproductive. But - 80% of the people who ordered a Countach got one with the massive wing. http://motoburg.com/images/lamborghi...lp5000s-06.jpg countach five-zero-zero-zero, make left traffic, follow the VW beetle at nine o'clock, 3 miles. Descend to 2000 and make your speed one-four-zero.

Quotes source post: 13852858

that's my old car. (I posted earlier in this thread.) You don't need gt3 liners. Just take out the 90 degree vents and cut a hole. Use gt3 scoops. Easy Peasy. I ran that configuration for a couple years. Mostly track duty. I can post more info if anyone needs it. -td

^^ this looks fine though I highly doubt it will have any effect on street driving. FYI, while we are on the subject, I did fit some GT2 brake ducts on my C2 briefly and it was quite humorous. It significantly increased airflow to the area right below my rotor, which would be relevant if I had GT2 sized rotors.

Quotes source post: 13852981

Yes. Or rather, no. Not higher limits. No limits :-) Om the other hand, driving today on cold damp roads with strong winds, at speeds such that you might get away with a warning in your area, with 205 front winter tires, I would have appreciated a front end that was more tied down. Thanks for the picture!

Quotes source post: 13853206

Yes, it probably seems I wasn't paying attention. I was actually paying very careful attention. I just somehow missed about 10 VERY interestig posts (which I've just now noticed) ... . Anyway, thanks much for letting us know! I read your thread, and it sounds pretty clear this helped keep your brakes cool. And where to cut is pretty clear from the all the pictures you posted. (Basically the same area that's cut away from the first to the second GT3.) One more question though - the 90 degree vents, what are those, exactly? Thanks again!

Quotes source post: 13853165

By some accounts, it cost the car around 30 mph. R&T was able to get a winged Countach up to 155. Without a wing my understanding is that the ~455hp 5000LP really could exceed 180. Making it clear to all the Lamborghini guys had no idea what they were doing. Except that they did. Indeed, they appatently knew exactly what they were doing. The wing was created by one of their largest dealers, and it did create downforce, a lot of it. Which was the last thing you wanted on a 180 mph, rear engined car with front-end lift. So the clever guys at Lamborghini tilted the wing so agressively that it created almost no downforce at all. It was basically just a big air brake. And they refused to sell it to you. You had to buy it from a dealer.

Quotes source post: 13851350

Thanks, first of all, for the very interesting posts!! There are of course many differences between Carreras and GT3s, though if a Carrera has the aerokit, the shape of the front end is very close, possibly identical if it also has a third radiator. With the stiffest of the sport suspensions (X71? I can never remember the name), the ride height is just 5 mm higher, if I recall correctly. Many Carreras also use the same size wheels and tires, the same brake ducts, and the same brakes. On the other hand, the most interesting comparison may be between the MkI GT3, which didn't vent into the wheel wells, and the Mk2, which did. What else changed? It seems the old radiator vent was blocked off on the MkII, and if one does this mod, presumably one should also block this off. That may have been the biggest change Did the bumper shape change much? It changed, but I don't remember a big change off the top of my head other than the headlight shape, which I would see mainly as a change in where the shape was metal and where glass, rather than a big shape change. Yhough I haven't looked for quite sime time, so this may be nonsense ... . If it's not nonsense, than venting into the wheel wells might account for a significant portion of any front end improvement. And I think small improvements in front end lift can make a significant difference. The 996.2 Carrera only has about 24 kg of front-end lift at 200 kmph,, so probably about 44 or 45 kg at vmax. The MkII GT3 has 13 kg, and I believe the C4S has roughly half as much as the Carrera. (All according to SportAuto wind tunnel tests.) By all accounts, the front ends of these cars feel more stable/precise/tied down at speed. And according to SportAuto, the vents into the wheel well was the aero highlight of the MkII versus the MkI. Alas, I don't have the numbers for the MkI handy, and this may be because I never saw them. I seem to remember I could not find SportAuto wind tunnel tests for it. Oh, and the front vent above the third radiator on the GT3 RS? Contributes about 3 kg of downforce. It's certainly possible that without this the car would be unstable, however. Because without it, it would have almost as much front-end lift as a Carrera. Anyone know how much front-end lift a MkI GT3 generates??? If someone has or knows where to find the press/launch materials ... .

Quotes source post: 13850660

And spend the money, I fear. Or these gauges and pots, are they affordable, like, say, an extra heat sensor for a data logger? Is there some software I can use to collect date from them on my computer, or perhaps an app for my phone? This mod is one of several aero questions I'd really like to know the answer to. Thanks!

Quotes source post: 13855156

I suspect that the downforce, and/or speed reduction were often a result of the installer. With the wing in a neutral AoA, the speed would show little compromise, and the downforce very limited. One could of course increase the negative angle of attack to create massive downforce, and huge speed reduction. It's been a lot of years, but I recall someone who knew what they were doing getting it setup for modest speed cost, and modest downforce, to basically minimize the effect where no downforce was really needed, as you mention, and as I alluded to in the rest of the unquoted post(30Lbs of downforce on a mid-engine car is useless). Perhaps the good folks at R&T, like everyone else in auto publishing don't know squadoosh about aero affects, and set the AoA where Lambo dealer/installer told them to set it, or left it wherever it was when they got the car. I really don't know.

Quotes source post: 13855113

On my car, they were right behind the radiators venting air downward before the wheel housing. That is, air passed through the radiators (and AC condenser) and a big piece of plastic vented the air down to the ground before the wheel well. They were easy to take out. -td

One more thing not considered in this mod so far, is the adiabatic affect of the air. As it's heated when passing through the rads, the air becomes less dense as it is hotter. Ideally, like the Daytona coupe, and my Ferrari Mondial that hot air would escape going up over the front of the car and not down where it will possibly create a pressure bubble inside or under, or around the wheel well(hard to say, without smoke/thermal testing). BTW, someone mentioned ducting it toward the brake intake duct? Not a good plan with warm low density air flow. Aero mods are tricky.

Quotes source post: 13850660

I understand there are no hard and fast rules, but if there is an answer that is usually true, would you expect switching from 205 section 17s to 225 section 18s (both with almost exactly the same diameter) would exacerbate or reduce this problem? Thanks again!

Quotes source post: 13855272

My guess is that the R&T guys simply took the car as it was handed to them, so probably with the standard wing with the standard installation as "fixed" by Lamborghini.

Not to hijack this thread, I might suggest that there is a lot of general technical knowledge with regard to vehicle aerodynamics available, in particular the treatment of exiting cooling air flow. See "Racecar Aerodynamics" by Joseph Katz for instance. Reinforcing some of the comments above, Katz' discussion of wings will reveal just how silly the Lambo folks were (as well as practically every street car manufacturer is) in the uneducated placement of rear wings. Placed within the disturbed air flowing over a chassis, a wing doesn't provide any performance improvements (Read the first part of that sentence before you disagree). Obvious differences between race cars and street cars aside, Katz explains how, when it's placed properly in conjunction with underbody design the wing can act more as a "lung", drawing and accelerating air flow under the car, where more force is created and distributed to the 4 corners, not just 2. More recent performance street car design seems to have caught on.

Quotes source post: 13852981

I just noticed something very interesting in this photo of the vents on a C4S (page 3, post 41). Am I correct that the vents point outwards? If so, they seems to have been designed not to cool the brakes, but to expel the air from the wheel arch. Maybe, if the Porsche guys were really clever, this even has a positive effect on the other air that is (or otherwise would be) in the wheel well. Anyway, as the purpose apparently isn't brake cooling, it must be drag, lift, and/or, just possibly, helping draw more air through the radiators. Probably doing this mod the Pelican way wouldn't work quite as well, since the air would not be directed in any particular direction. The best way would probably be to us C4S (or 40AE or Turbo) wheel well liners, provided they are compatible with the neigbouring parts. Shame we still can't be sure this would have aerodynamic benefits on a Carrera, given the different bumper openings, ducting, and slightly larger radiators. (And there remains the question whether the GT3 method, on a car with a very similar bumper, ducts, etc., just improved brake cooling or also has aero benefits.) P.S. Sorry not to include the photo here. For some reason it does not reappear when I reply to the post

Understanding that 997 Carreras also vent air into the wheel wells, anyone know if they also direct air outwards as on the 996 C4S, Turbo, etc.? Or do they direct it at the brakes, like on a 996 GT3? Or perhaps something completely different ... ? Thanks!

Quotes source post: 13852981

I heard this, And thought this: and got all .

RS: Don't know about the 997's but the C4S vents are definitely directed out of the wheel well and do not appear that the air flow would have any affect on brake cooling.

Strath: That would probably affect aero as well!

Quotes source post: 13859815

All the fast kids are doing it. Something tells my punching holes in the sheet metal would effect resale value. Maybe I would call them "speed holes"

One of the fastest, and most notable small aircraft of it's day was the early Beech Bonanza. As it grew, and got ever more higher HP engines, at a point the plane started having trouble shedding heat in climb. The solution provided by Beech, and approved was to cut louvers in the lower gill doors to release heat from the cylinders below the engine. Of course, not a direct correlation, but worth looking at: http://thumbs4.ebaystatic.com/d/l800...68227163_1.jpg From the factory, these gill doors were just a flat sheet of metal. Punching the vents in them improved the cooling and had little to no effect on the aerodynamics. It was either luck, or serendipity that this worked as well as it did, because I don't think there was a ton of engineering done. They basically went out and punched some slots in the gill door, and fitted it back to the same plane and took measurements.

Fast kids might not care about resale because they will probably wrap the car around a pole or other stationary object!

Wildbilly, on your C4Ss, do the vents from the radiators also lead to openings below the car as on Carreras? Or are they blocked of like on the MkII GT3? Thanks!

RS: There are openings beneath car which if you reach inside towards the front of car you can feel the rad fan blades. I have not felt in this area to verify radiator air flow. However, I do know if the fans are running you can feel the warm air exiting the wheel well vents!!?? Could it also be a way for the air that enters to center grill to exit the car? After all these noses are designed for the center radiator.

Quotes source post: 13860924

I installed the center radiator kit a while back. I didn't buy the whole kit as I wasn't happy with the intake boot ducting. There is no ducting out the back side and it's left to discharge down and back under the car. i wondered about the effect of the air under the car now, but before installation, there was just that indented rubber insert in the front bumper, so I knew it couldn't be much worse than bone stock. I have no idea about the airflow past the radiator, but presume that it just flows down and back. I could be entirely wrong though. However, it does not flow to the side as far as I can tell. The front shape of the frunk well is tapered back somewhat, but not V shaped so it would promote flow to the sides.

Below are pics of my solution about radiator/fan bracket mods from 996 mkI, where they're orginally veted downwards ahead of front wheels. As 997 GTx and Cup/CupS (plus also some 996s) cars have vent to wheel wells, the solution must have some benefits over the initial set up of 996/986. I haven't wasted much of thoughs about the theory (don't think too much, it hurts your head.. ), just copied working solutions. Study factory solutions from racers, there's lot to be gained if you're not hysterically into keeping your car 100% original. While the mkI radiator/fan bracket has a diagonal brace behind the fan, later models do not, the bracket is almost square for the vent to open unobstructed backwards. So I cut it away and spotwelded it inboards. And the frame is square... Next step is to cut out and form the opening to fender liner, v2.0. v1.0 had two triangular openings both sides of that diagonal brace, but now I can cut out a bigger and square one. Equipped of course with a wire mesh screen like racers have. Air will be quided out from wheel wells race car style in this v2.0. Another reason for doing this v2.0 is to fit 10x18 et37 wheels with 265/35-18 MPSC2s. With 40 mm LCA shims. Well, not really 40mm of shims, just 25mm and 997 Cup LCA inner ends, which are 15 mm longer than 996's.

Quotes source posts: 13860924, 13861334

I'm a bit confused. My understanding is that on a C4S or 40AE, the air that enters the center opening in the bumper is mostly blocked by a very obstructive black plastic grill from going any further. And any air that makes it through has no where to go but down. But if you have a turbo, or a 3rd radiator on a C4S or 40AE, then there is an open grill instead of this obstructive one. The air that flows through it then passes through the radiator, and then has pretty much no where to go but down (unless you have GT3RS style openings above). For both the obstructive grill and the open grill, see post 47 in this thread: https://rennlist.com/forums/996-foru...it-work-4.html And in neither case could any air enter a duct that leads to the wheel wells. Or indeed to a duct that leads anywhere. Make sense?

Quotes source post: 13898784

Don't know about the diff in the 40AE, but on a 99 C2, the bumper has a block off center duct which is removed. The air then goes through a duct, past the center rad, and exits downward. One could put a grill on from a car with tip, which has a center rad as standard. I chose to leave the center opening bare for now.

Barely read through any of this but I can tell you my C4S wheel liners have open air fins behind the front radiators. Not sure if that was a 996.2 deal or what. The center inlet on the C4S/TT front bumper barely lets any air in and there is no where for it to go but down without a GT2 conversion or center radiator (which both C4S/TT don't need)

If you notice all cars that have relief for pressure in the wheel well is at the top of the fender - if you open that area up

I did want to just pop in and leave this here for those interested. This excerpt is taken directly taken from the Porsche Intro book for the 987: Also, it's interesting that frontal area was increased which is usually bad. However, with the 987 improvements the drag coefficient was actually lowered. Not sure how much of that improvement was the vents in the wheel wells, but I'm sure it accounts for some of it.

Interesting book! Were does one get one of those?!?

Quotes source post: 13904848

Very interesting post as well - thanks! Do you know if the 987 (or the 997)'s vents into the wheel well are shaped and positioned like the 996 turbo's (as shown earlier in this thread)? Or like the 996 GT3s? Or ... ? Thanks again!

Do other 996s not have wheel liner fins like this?

C4Ss and Turbos do. Probably 40AEs - not sure now (someone may have mentioned this above). The rest do not.

Quotes source posts: 13906001, 13906009, 13906083

Books are sold by Porsche during the release of new models. Usually you have to buy them close to the release of the new vehicle, but PDF versions do end up floating around. You're welcome! They�re more like the C4S and Turbo�s than the GT3�s. GT3 makes use of additional brake cooling deflectors, which necessitate the open airflow through the wheel housing liner. This photo shows a C4S and Turbo style fender liner I believe�

Quotes source post: 13908580

40th AE's have those fins - yes.

Quotes source post: 13899278

No personal opinion or experience on this myself but this informed video just popped up in my youtube feed and it's super interesting given the topic of this thread.

Quotes source post: 13910380

Again very interesting. I don't suppose you know if the relevant part of the fender liner from a C4S, 987 or 997 could be used on a 996 C2? Thanks again!

Been following this thread, and there are some interesting things here. One of the things I see being overlooked to some extent. There's two sides to the drag ratio, one is the leading side of the equation where air is pushed through or around structures. The other side of the equation is the air extraction or the 'vacuum' side. Air recombines after leaving an area of disturbance. This side is often given short shrift. Again from an aerodynamic theme, the original P-51 Mustang aircraft was water cooled. This allowed it to have a very high volumetric efficiency. One of the byproducts was the ducting for the radiator(seen on the belly of the fuselage, a snorkel facing forward). The original design was done poorly, and caused a pressure bubble to be formed in the inlet. Once it was reworked, and the adiabatic effects of heating the air were taken into account, the venting of the hot exhaust from there actually improved the speed of the plane! Back to cars, I once owned a car called a Cord 812. Along with the Chrysler Airflow, it was one of the first cars to make serious use of aerodynamics. It had contoured fenders with hideaway headlights. Back sloped windscreen. No running boards(first car without). Flat under-floor, and even the door handles were teardrop shaped. So, it's nothing new, but it is a tough thing to solve. Without a wind tunnel it's so hard to prove out, even something that looks like a solution, may not be. So, don't get too wrapped up in just the venting of the intake air. Also consider more the effects as the air is warmed(or not) and how and where it recombines after going around the obstruction.

Quotes source post: 13911188

Yes it can, in conjunction with the other pieces. The 40th Anniversary cars were essentially C2’s, which had this setup. If you want I can put together a parts list with our Pelican part numbers. Let me know.

Quotes source post: 13912906

Could I please get a parts list, I upgraded my bumper and feel some underbelly parts are missing. Thanks!

Quotes source posts: 13911188, 13912930

Looking at it now, there might be subtle differences in the way that the forward edge meets the bumper if the car does not have the C4S /Turbo/ 40th Anniversary style bumper. There will probably be a few different variations of this �conversion� whether you want to go with the full conversion including the bumper all ducting around the radiators, and the fender liners. Just FYI, the non vented fender liner is a one piece liner while the later vented style uses two pieces to accomplish the same thing. See below: Vented style: I don�t really know if one could simply adapt �just � the vented fender liner, to really get the most out of the mod you would want to go all out. I�ll look at what is involved and let you know if it�s worth the time. I'll report back soon!

Quotes source post: 13852981

This is the same as the 40th AE - it's just some vents behind the radiator that vent into the wheel well. Not exactly rocket since. You could just cut some vents with an exacto/stanley knife. BUT as poster above said - unless you are going really fast i.e. a race track - i don't think it's going to make a difference.

Quotes source post: 13912906

I'm also interested. Definitely if it can be made to work without changing everything from the bumper to the wheel well. Maybe if can't. So there's interest for Carreras who have a turbo front bumper, and for Carreras that don't (yet) have a turbo front bumper. By the way, it sounds like the discussion is now focused on C4S/Turbo wheel well liners. I don't suppose the 987 or 997 parts would work? Finally, I understand the Turbo and C4S still have the same opening on the bottom of the car as the Carrera. (Or is it a similar opening with a different shape?) What about the 987 and 997? Thanks!

Quotes source posts: 13912969, 13912969

You could. But they wouldn't direct air outwards like the C4S/Turbo vents do. So rather than making things better, they might welk make things worse. But if you are going fast, like on a race track, then it probably is going to make a difference. At 124 mph (200 kmph), the TT has 6kg of lift in the front, versus 24kg for the Carrera, around 12kg for the C4S (due to a smaller lip spoiler than the TT - and whereas I'm sure of the other two, the C4S is from memory), and 13 for the GT3. Small differences, it seems. But C4Ss and Carreras with the aerokit (identical to the GT3) are said to be recognizably more tied down in the front at speed - which is consistently reported as a very good thing. Of course, it's not all because of the vent change. But I'm pretty sure it helps. Indeed, the spoiler part of the bumper on the GT3 extends even further down than the TT's, so all else being equal, one would expect the GT3 to have less lift than the TT, not more.

There is always the question, will venting air from the wheel wells in the same way as a TT/C4S/40AE, or a 987 or 997 work if you don't have the same front bumper and bits in between. You probabbly don't have to have the exact same bumper, but I had a look at pictures of a 987.1 bumper from a non S Boxter, and it seems to me it is very similar to a 996 bumper. You wouldn't mistake them, of course. But it seems to me that air hitting the car at any given height and any given distance from center will be directed in roughly the same direction, and the left and right openings have roughly the same size and position. So if the bits between the bumper and the wheel well vents are similar, then 987 (and probably 997) style vents would work. I also had a quick look at wheel well vents in s 997, and they look rather like the C4S vents. They also direct the air horizontally outwards. Though the vents together fill a rectangular space, instead of a triangular one. They are fruther inboard than I expected, though this may also be the case with a C4S. Anyway, here are some 987 pictures I found:

And here for comparison is a rather nicely colored 996 bumper (no, not mine - much easier to find pictured online that to go out and take them):

Notice the vents for pressure relief

Hi all, I registered so I cold take part in this thread.. My question is, does the 996 GT3 have the upper wind deflectors seen here , but without vented wheel arches? How much air are they pushing about inside the wheel arches? I can see that they'd make it all look much tidier, however. I'm looking to get the 997 wind deflectors (99757523191 and 99757523291) on my 996 C2, but am not sure if 996 GT3 wheel arch liners will do anything. I would rather do this than cut holes in things (the car is going in for work soon, so I was planning on getting them to do it).

Quotes source post: 13916126

This is the list I got for individuals who have done the turbo front bumper conversion (FYI, pre 02 cars will be different form this list): Front Bumper, and underbody: Front air duct CLICK HERE x 1 Screw 4.7x1 (Previous part #N90648702) CLICK HERE x 4 Wheel housing CLICK HERE X 1 Wheel housing CLICK HERE X 1 Wheel housing liner CLICK HERE X 1 Wheel well molding CLICK HERE X 1 Wheel well molding CLICK HERE X 1 Air duct CLICK HERE X 1 Air deflector CLICK HERE X 1 PET is kind of weird on those last 2, so not 100% sure on them. Radiator pieces: Air duct CLICK HERE X 1 Other air duct CLICK HERE X 1 I am not sure if you can use the 987/997 liner in a 986/996. I would think they could be made to work, but I think you'll need the fasteners from the 9x7 liner. I recall the 9x7 cars had torx screws where the 9x6's had plastic rivets. I'll look more into this.

Quotes source post: 13924910

Yes, the 996 GT3 has the upper wind deflectors seen in the link you posted - it is a picture of these wind deflectors on a 996 GT3. The 996 GT3 wheel arch liners have an opening that funnels air leaving the radiators directly into these wind deflectors. Furthermore, I believe that on the GT3s, the opening where radiator air is blown downwards on a Carrera is closed. This is undoubtedly better for cooling your brakes than either using the C4S/TT/40AE vent setup or doing nothing. On the otherhand, I'm pretty sure it's worse for drag and lift than the C4S/TT/40AE vent setup, which is very different. Not sure how it compares for drag and lift to the standard Carrera setup.

Quotes source post: 13925495

Great, thanks for the info. I want to improve air flow to my front brakes, so this sounds good. Has anyone put 996 GT3 wheel arch liners in a C2.1? Looking at the parts diagrams, my car has a one piece liner: And the 996 GT3 has a two piece, so I'd need to buy parts 1 & 2? Looks like it still uses the ducts / air damn under the car (parts 5 & 9). Thanks again.

Interesting. I do not see any difference between the Carrera and GT3 liners where the cutout venting air to the upper brake ducts is. The shape really looks exactly the same. And part number 3 in the top picture makes me wonder if the Carrera liner isn't actually two pieces which are sold as one. Perhaps the picture is the 996.1 GT3 and the cutout is only on the 996.2 GT3 or the RS?

Indeed, I can't work out what the upper deflectors on a 996 GT3 do; It would be really helpful to see some photos of the arch liners on a 996 GT3. Perhaps unsurprisingly Google isn't very helpful.

pet isn't perfect. search the part # for actual image. gt3.1 differs from gt3.2.

Quotes source post: 13935448

+1. PET pictures can be misleading.

Apologies to bump an old thread but I never saw anyone take the plunge and actually fit the 996 GT3 liners and 997 upper brake ducts. I did quite a bit of research to verify this before fitment, as to concerns about drag etc, any negative effects must be minimal as the 997 GT2/GT3 also vent along the inner fender and use the radiator exhaust to cool the front brakes. Below is my how to, everything bolts up with just a little trimming to the new liners. Part Numbers: Left and Right 996 GT3 Fender Liner: 99650412392, 99650412492 997 GT3/GT2 Left and Right Brake Ducts: 99757523191, 99757523291 Plastic Rivets, Qty:4 99950749740 2 Zip ties No other hardware is required but you'll probably break a few of the expanding rivets: 99950749740 1. The old fender liners must be removed first, there are 5 rivets and 4 screws to remove. I believe most people have already done this job at some point. 2. The plastic 90 degree air ducts must be removed next, they are located behind the radiator fans and are held in place by 1 circlip. They direct the output from the radiator fans out through the triangular holes on the bottom of the car. To do this you can either remove the bumper, and then the radiator support bracket or just cut the 90 degree ducts into pieces and remove. The 996 GT3 uses the same radiator and support bracket, confusingly PET shows the 90 degree duct fitted but there is no way this works with it in place. You will want to move the fan resistor from the old location to the new radiator exhaust location.. 90 degree duct removed: 3. Next we must trim the new fender liner to match the profile of the old liner. All of your work will be on the lower outside corner of the liner where it meets with the bumper, you are adding a .75"x.1" notch and removing a flange near a mounting screw. Just overlay them and trim to match. 4. Trimming is completed and now fit the liner reverse of removal of the old ones, take note the triangular opening is now gone, a tab now overlaps the bumper at this location. 5. The brake ducts are a bit more work, as the mounting holes are not provided. I utilized the existing holes in the duct as a guide and added the holes needed to the new fender liner. The aluminum bracket can be zip tied to the chassis brake line mount. The duct and liner are joined with 2 plastic rivets. 6. The ducts must be trimmed around the tie rod, I have removed vary little material, will check later for the tie rod rubbing to see if more needs to be removed. The tire/wheel does not rub yet, but may require trimming in the future. Thats it! It isn't very hot in Texas now (80* today) so I'm unsure whether enlarging the opening in the liner will be required, I did notice the fenders and trunk got pretty warm which the GT3 guys complain about but car seemed very stable >80mph, and I still have the OEM suspension at 106000 miles!

I did the cut-open modification on my 996 C2 and noticed that it did help coolant temperatures on the track (at least on the dash gauge) and I assume it helped brake temperatures but did not measure. I saw no change in front end stability on the track. I used wire mesh and pop riveted it to the fender liner rather than cutting a bunch of slits in the plastic.

I just did a video on venting the inner fenders and installing the 997 GT3 upper brake ducts You Tube

I did some of these mods on my wife's Land Speed 996. I was hunting for Aero benefits more than anything, and did notice some gains when the air could pass straight through the radiators and into the wheel wells. Ultimately I was able to block one main radiator off completely, as well as the center radiator and things were fine in the standing mile for engine temps. I knew at Bonneville on the longer courses we'd not be able to do this, so I was hunting for a resolution before we went there. Ultimately I ended up removing the fans, and opening up the entire discharge area on that car, and it even worked ok omg the street, but we never sat still in traffic with the car.

Was this on a .1 or .2 car? I saw someone ask about the 2 piece vs 1 piece fender well but didnt notice a definitive response. I have a .1 so I assume I to purchase the 2 pieces of the gt3 fender liner? Apart from any aero or brake cooling, I really want to block the downward venting fans. I have a higher hp car and the fans are quite active when creeping slow. It tends to blow dirt all over the place, which gets sucked back into the rad fans. Terrible design in that respect.

The gt3 liners fit on the mk1 cars with no mods. I have done this on my gt3ish. I would also reccomend the gt3 air diverter piece that directs it to the brakes. It gets a little pricey but the benifits r worth it. Hopefully u already have a 3rd rad but if u need more cooling upgrade to cfs rads or go with the turbo rads. The later may require a turbo bumper.

Quotes source post: 17784773

De Jeeper and Rob, thanks for revising the thread. Very helpful info.

I run 1radiator fan only and heavily vented liners. Not saying it will work for you, but it does for me. Have sat in moderate traffic and multiple hour street drives with no negative affects.

A lot of good rabbit trails attached to this thread on cooling and aero ideas. Gonna take awhile to get thru all of them.

Are you running stock rads? I need to cool down the ls3 in the back so need all the help I can get.

Quotes source post: 17785439

Yes, I have run stock radiators over 14 years of DE, but am running a 2Qt deep sump which helps with cooling for the first 20 min. However, as soon as LN rolls out their Oil cooling kit, and I know whether it will need the 3rd radiator spot or not, I will move towards adding 2 or 3 CSF radiators. My set-up worked effectively for years, so I never Needed to upgrade the radiators. But at this stage, the car is 19 years old and could probably use a new set. Don't know much about cooling an LS3 so my response may not be any help.

Quotes source post: 17785439

My knowledge on LS swaps is limited to the research I have done for my application (a lot of track work). My conclusion is inability to manage heat is a major contributing factor in the failure of some engines on track. If it were me, I would run a turbo front bumper and ducting with all 3 turbo rads. For the center rad, I�d run the GT2 chimney which exhausts the center rad airflow up over the hood, this seems like not only a good idea for cooling but also aero. For a street setup, big fans with effective shrouding would also be something to consider. Lastly, if you want to get crazy with it, my plan for if the above didn�t work, retrofit an intercooler water sprayer to all 3 rads. If all that didn�t work, it would get pretty hard from there.

Quotes source post: 17785984

I haven't properly tracked the car at this point, but have done "spirited" driving, 4+ hour mountain road trips, etc and no issue with cooling as long at the car is moving. I do have a CSF 3rd radiator, so likely that's helping, but looking for anything to assist cooling. The issues arise more in simple stop and go traffic and I'd be worried about cooldown after a track session. Looking to go with higher capacity fans and PMW controller for peace of mind. I still have the stock rads so CSF upgrade maybe as well. I did see an old thread where someone fit 996 turbo rads on a c2, but it required a bunch of modification - not sure if that would gain much vs a c2 CSF rad? Given my car seems to be on fan more in the city and at a stop, hopefully venting into the wheel wells will stop dust and debris from being recirculated back into the radiators as it does currently. I seem to be accumulating hay stack regularly, which probably isn't helping cooling. If anyone is fiddling with this mod, could somebody take a quick and dirty measurement of the stock c2 rad fan diameter? Need to figure out how much fan diameter I could fit if I replaced it with a spal or something.

The turbo rads are considerably larger than C2. I would run stock Turbo rads over C2 CSF. I can check and see if I have the fan/shroud assembly I pulled off and let you know dimension if I didn’t throw it out.

Quotes source post: 17826338

I did a quick comparison of cubic inch dimension of a couple vehicles - not that this is the end all, but shows volume of cooling surface capacity and could be a decent indicator. A 996 C2 with the 3 CSF radiators is better than a C7 corvette and not much off an improved after market C7 radiator. The turbo car does have more CI for sure. just not sure I could fit those in a 996.1.

Im pretty sure that user lowpue had turbo rads stuffed under a mk1 aero bumper. I think it flexed, bulged, it a little but they got it to work. we use spal fans on out jeeps and they push some serious air but so do the porsche units. Not sure if the swap would be worth the effort?

Semi-resurrection of a not terribly old thread. I am looking for ways to reduce front end lift on my C2 targa and the radiator air exit mod appears to me to be a good way to do it. 40AE cars have vented wheel well liners, and 997's do too, so that leads me to think that Porsche engineers saw a benefit as well. In fact the 997 takes the wheel well exit to a whole different level (see pics). Here's where I am at the moment with all of it. Option 1: 40AE front wheel well liners and rubber moldings (they're unique to the 40AE) should come close to bolting straight onto my car. Yes I could just cut slots in my liners, but the 40AE (and 997) pieces specifically push air towards the outside. Plus the vents will keep gunk slung off the tires from getting into the fans. 99650412300 Wheel-Housing Liner (DRIVER SIDE, FRONT) 99650412400 Wheel-Housing Liner (PASSENGER SIDE, FRONT) 99650450302 Rubber Moulding (DRIVER SIDE) 99650450402 Rubber Moulding (PASSENGER SIDE) Option 2: GT3 liners + duct piece to direct radiator exit air to the brakes. I think money could be saved here by just chopping the inner edge off the stock liners. Part numbers have been previously posted. In both cases the fan shroud will need to be modified to allow radiator air to exit in the desired direction rather than having it all directed straight down as it is now. I looked into 40AE radiator shrouds, but the radiators, fans and shrouds are all different part numbers. I believe they are bigger, which I suspect would make it very hard to modify a 40AE fan shroud to fit my car. Some pictures below that I collected in my research. 997 fan shroud showing giant opening into wheel well. The WW liner mates right up to it. Hard to see in this pic but there is a small downward exit path as well. 40AE underside appears to show underside exit for radiator air. 40AE WW liners. 40AE radiator shroud. Hard to see but it looks to me as though it has a significantly smaller opening than the 997. If anyone has a better picture please post it!

40AE/C4S/Turbo use the same front bumper and wheel well liners - those part#'s you have listed. You would also need the rear half of the Turbo wheel well liner: 995-504-203-08 and 996-504-204-08. That said I don't think those will work on a C2/C4/GT3 front bumper, the turbo bumper is much "squarer" at the bottom, it doesn't curve under the car as much. So the front part of the wheel well liners is much longer than the C2/C4/GT3 wheel well liners. Also the Turbo liners are made to bolt up to the Turbo radiator supports.

Quotes source post: 18207001

996.2 has 2-piece wheel well liners. The rear part number doesn't change between standard and 40AE. So that should be good to go. You're probably right though that getting the front edges to fit decently might pose a challenge. Not a direct bolt on piece. Darn. The inside edge exit + GT3 "ducts" might be the better solution.

My gt3 inner fender set up cost a small fortune but it works. If u really want to hold the front down buy diveplanes from demonspeed and mod the center rad to vent over the frunk.

Only crazy people do that kind of stuff.

Quotes source post: 18207096

ill take that as a complement.

Quotes source post: 18207083

Looking good. Is that your fresh paint?

Quotes source post: 18207923

Thx, just the front bumper. I just finally washed the rest . Since i track the car its kinda a 5 footer.

Wow that all looks so clean! Is there a template for the bumper cutouts as you have? Did you do the full GT3 fender liner replacement or just lower piece with cut out? Some seem to have grille slats also? Sorry, hope you don't mind the questions. Attempting to do my 99 C2 correctly ......................... Godspeed! Dave

Ok, I apologize, looked only at last post. Went further up to see part numbers and such! Thanks

Quotes source post: 18210328

Np, i used all the gt3 parts. For the center rad i used the factory rsr chimney but made the rest of the parts to alter the direction of the air flow myself. For the cut outs i had my body shop guy go off the rsr mk2 template but they need to be adjusted for the mk1 headlights. The templates r on rennlist somewhere, sorry dont have the link. More details in my build here. This mod is near the end. https://rennlist.com/forums/996-foru...-the-dust.html

Thank you..................

thanks for all the info in this thread. when venting the fender liner, any reason to not leave out the rubber air deflector behind the fan all together? instead of cutting vents into it (like in the Pelican Parts article)? or does it need to stay for some other reason?

Great question. I'm trying to figure that part out as well. I was under the impression that the 996 GT3 shroud would be different, so that the air being redirected towards the brake rotor would be aimed at the opening in the GT3 fender liner. However according to PET the part numbers for GT3 and 996 C2 are identical. Which makes me wonder just how much air is actually being redirected! I haven't found a picture of the actual GT3 part yet to verify. 996 GT3 99657534104 Air Duct (DRIVER SIDE) 99657534200 Air Duct (PASSENGER SIDE) 996 C2 99657534104 Air Duct (DRIVER SIDE, FROM YEAR 99 UP) 99657534200 Air Duct (PASSENGER SIDE, FROM YEAR 99 UP)

I removed it and I cut the fender liner closest to the tub instead of making the slotts, works great. After cleaning the radiators this spring I also made the duct in front of the radiator seal air tight(or as close as possible) to the radiator, this makes a great difference too.

The air ducts r what clips in the control arms. The fan shroud is deteted in the gt3, fender liner is 2 piece and blocks the air from going under the car. It forces it to the inner wall of the wheel well where an additional scoop clips to the rad tubes and directs the air to rotors.

Quotes source post: 18225174

I love the concept! But I find a part number in PET for the shroud under the GT3. Makes me question. I'd also love to see pics of the GT3 fender liner. From what I can tell it is a simple matter of hacking a chunk off the 996.2 piece.

Quotes source post: 18225208

Well the fan on the gt3 i took apart had no shroud. I am talking about the rubber boot behind the fan not the scoop in front. Yes u can just cut the mk2 liner but u need to close the off the bottom and install the scoop that clips on the coolant tubes.

I've returned to this project. Which project? Several different venting options are mentioned in this thread. To avoid confusion when I discuss parts and problems, etc. below, I'm aiming for a conversion where the air goes in a C4S or Turbo bumper, through C4S ducts to the radiators, and then after the radiators goes into the wheel well through C4S vents (which direct air outwards, unlike cutting a hole in the wheel well which vents it towards the tire). I prefer this option because it results in front end lift that is either almost as low as a GT3s (with the C4S spoiler) or even lower (with a Turbo spoiler). But instead of the very low, fragile GT3/aerokit bumper which makes you terrified to perpendicular park, you gut a higher bumper (though you still need to be careful). Furthermore, Porsche says again and again that if you use the aerokit front end, you must use the back end too (meaning a big wing), or else the aerodynamics will be unbalanced. And adding this wing may be a great thing. But it is expensive. And it does add weight in the worst possible place, unless you can find a (much more expensive) carbon version. On the other hand, the C4S front end is combined with the normal C2 back end on the 40AE. And if that's good enough for Porsche, it's good enough for me.

Quotes source post: 13924922

As mentioned, I've returned to this project (as defined in the previous post), and starting with this list posted by Pelican Parts (copied above), I ended up with a much longer list. But I'm hoping it's not all necessary. To get an aerodynamic result very similar to that with the C4S and 40AE, there are two clear must-have parts. The C4S bumper (with the C4S spoiler). And the C4S wheel well vents that sends air in the right direction. Unfortunately, if one goes through the PET, each of these parts are connected to lots of parts used only on the C4S and in some cases the 40AE and Turbo. So many parts that it would be cheaper to buy an aerokit bumper, plus a bunch of spare aerokit bumpers to replace those you bang up while parking. But do you need all these parts? Well, I've tried to use the wheel well vent piece (part number 996 504 123 00 on the left side) on a Targa, and my local Porsche specialist found it impossible to even fit it without the C4S's radiator mounting bracket. Which suggests that to do this, you need C4S radiators. And fans. And airboxes (the surround behind the radiator and fan). And other brackets, etc. And the C4S a/c condenser. Which seems to require lots of C4S hoses and pipes. Etc., etc. Unless ... . Assuming there's no way around the C4S mounting bracket, the question is whether you can't attach all the normal C2/C4 engine cooling and a/c hardware to it (and then have the C4S ducts in front of them). I fear not for two reasons. First, does the C4S bracket hold the radiator, etc., in the same position? If part of the reason it leaves space for the wheel well vent is that it moves the radiators forward or positions them at a different angle, that seems like it could cause problems even with the C4S ducts installed. Does anyone know if there is any difference in radiator positions? Second, the C4S radiators are bigger, and the C4S ducts presumably have larger openings at the radiator end. (True??) If so, then combining these ducts with smaller radiators could have two problems. First, some air could get around the radiators, with adverse effects for cooling and who knows what aero effect. Second, some air could be directed to a part of the radiator that it can't flow through, with the same kind of risks. Does anyone know if the ducts in fact open to a different shape at the radiator end? (And if so, I don't suppose anyone knows if the air nonetheless can't avoid passing through the radiators and won't hit a larger area that it can't flow through than on a C4S.) Or perhaps someone knows of a good way to modify ducts so that the C2/C4 radiators work? (I believe I mentioned earlier in this thread the recommendation to cut open the top of the C2/C4 ducts at the bumper end. Unfortunately, I don't know exactly how this should work. And I struggle to imagine how this can result in a duct that both captures as much air as a duct actually designed to fit the bumper (the C4S duct) and funnel it smoothly and quickly towards the radiator without messing up the aero. But maybe I'm missing something.)

Like I wrote earlier the front ends can be swapped if you use all the parts that go with that front end. Can I ask what's your goal here? There are aftermarket bumpers that look like C4S bumpers that can be installed on regular cars with no changes (according to the aftermarket manufacturers) if you want a C4S looking bumper. It's easy to cut holes in the fender liners to vent the rads into the wheel wells if that is your goal. It is possible to put an OEM C4S bumper on a regular car with the stock radiators with some fiddling. If you are wanting a full C4S front end you are going to need all those parts in your list and more. Hint - use the Turbo PET because it's less confusing.

I haven't really followed this thread carefully as I have no intention of making this mod. I do recall the video below that talks about what the creator claims is a bit of an aerodynamic miracle of the 996 design directing radiator air exit to under the wheels using the air deflector in font of the wheel wells. This reduces the radiator air drag from the typical 10 or so percent to less than 1%. I'm not sure whether this has any bearing on this discussion, but posting just in case. You Tube

Quotes source post: 18647716

Thanks for the Turbo PET tip! As per my first post yesterday (and my previous posts), the goal is purely aerodynamic. The aftermarket bumpers are copies of the Porsche C4S bumper and if installed the same way, you get the same result (to the extent they are good copies). At least, I haven't found any aftermarket C4S copies that come with matching ducts, etc. - if you know of any, please do let us know! Cutting holes is easy. As per my previous post, I want the air to enter the wheel wells directed outwards, exactly like on a C4S, 40AE, Turbo, etc. That is not easy. I have found no solution other than using the original wheel well part. (But if you know of any ... .) And yes, as per my previous post, I know there are many more parts, having put together a "much longer" list. I was inspired to write the last post after starting to check prices of more of the items on the list. I had thought this project would be affordable because I knew the parts that I expected to be among the most expensive - the bumper, radiators, condensers - were affordable. I figured that something like an a/c hose ("line") couldn't be more than, say, 1/3 the price of a condenser. Turns out they may be more than 3 times the price of a condenser. And there are many of them :- ( (With luck, the C4S only needs different lines to go around the 4wd hardware and the differently shaped trunk. But the PET doesn't specify which the 40AE uses, so I don't know.)

Quotes source post: 18648982

Good video. Most folks just aren't fast enough for any aero to benefit them on the track. Mechanical grip with a proper suspension set-up, sticky tires, dureable brakes and lsd is much more important. No question aero looks damn good, but its irrelevent on the street unless you are looking for aesthetics. But who isnt?

Quotes source post: 18649303

True. Except on streets where it's even more relevant than on track. Like an Autobahn. Sometimes the car feels almost locked down no matter how fast I go. Sometimes the front gets light and nervous above 200 kpm (124 mph). Previous cars (not P cars) didn't. Seems most likely due to cross winds, but I suppose it could be due to poor road surfaces, or something else. Anyway, I don't like it, and hope to change it.

Quotes source post: 18649000

Hmm, seems I must have been mistaken about this. If this were true, the C4 would also use different lines from the C2, but it doesn't. So it would seems that if you have something else specific to the C4S (ducts? radiators?). then you need the C4S lines. Probably not condensors, b/c I replaced condensers on a C2 I briefly owned, and if I recall correctly, I was annoyed to learn I paid too much b/c my local specialist accidentally ordered C4S condensers. And they seemed to work fine ... .

My c4 narrow body 2003 only vents downward, I have CSF radiators, and I have the center rad. (Got a deal and couldn't pass it up) With the low temp thermostat I run dead on 180 F all the time now even in traffic. I also did the fan resistor change out and used 100W heat sync'd resistors. I found 1 dead resister while swapping the radiators so just replaced both. Interesting bit I found while working on the car, I have a piece on the belly pan thats right at the the rear cross member, it wasn't in my shop manual, its got louvers in it that seem to guid air up around the bell housing, I assume to help keep the clutch cooler. It attaches between the under-tray large sections and the cross bar.. I went to the dealer and had them look up the number and its a GT3 part.

Quotes source post: 18649511

Check out Demons dive planes. Heck of alot cheaper than reworking the front bumper. https://www.demonspeedmotorsports.co...ords=Dive+plan As a side note, if you don't like the idea of dive plans, check into the multiple front spoilers they have for just about every bumper. I have one of their GT3 front spoilers. Haven't put it on yet but probably will this spring. Here is the point, aero is nice, but mechanical set up is better before you play with aero. If you are going to drive at 125, you better have a solid, well balanced set-up first. I have done over 1200 laps at Road America on the straights between 130 and 145 without aero. Sure, at 145 in a cross wind the front gets a little light but its predictable. Tire pressures and tires are also very important. Over inflated tires at that speed are traveling on a very narrow patch.

Quotes source post: 18649303

In my opinion, is not just a question of aero benefit on the track. The aero management in these and any high performance car (and in almost every car) has a lot of engineering behind it and direct impact in thermal management of the engine, drag reduction, stability even fuel economy Maybe small modifications like opening some vents doesn't have a big impact, but others, like removing the whole air duct behind the fans can mess totally with the way the air is managed around and under the car and have really implications that you can notice (more difficult to cool the engine under high demand, vibration in the wheels, brake fading appearing sooner due to a poorer cooling)

Quotes source post: 18649617

Bingo. Our cars slice thru the air at speed. Well designed. Quite frankly, I didn't want to mess with aero after I got the right mechanical grip. Didn't want to mess up.

Just soemthing I noticed when I did the 3rd radiator ,,, when you cut the hole for the ductwork it actually creates a pretty fail sized area to push down on the nose. Not ginormous but I'd say a 18" x 10 inch area of new surface area.. the rearward flow is limited by the size of the air reliefs that are already there.. And I kinda like the new silver area the radiator gives the slot across the bumper. Looks more functional.

Quotes source posts: 18649617, 18649628

My views are similar. So I'm reluctant to go with a solution that was not designed by Porsche or someone else whom I'd trust to design and test it well, e.g. Manthey, Ruf, ... am I missing someone? And I fear that if you have a C4S bumper and Carrera radiator and somehow cut/twist/modify the ducts (whether C4S or Carrera) to direct air from one to the other, you are playing with the aero almost as much as if you cut/twisted/modified the bumper itself. On the other hand, I haven't had a good look at either kind of ducts or radiators or their position in the car, and while I understand a good bodyshop can work miracles with a metal fender, I have no idea what they can do with a plastic duct ... .

I resurrected this thread a while back and rambled a bit about 40AE vents and 997 vents and so on. I finally got to a point where I wanted to have a go at venting into the wheel wells on my own car. The first iteration was a bit of a bollux. I didn't just want holes in the liner because I didn't like the idea of the wheels heaving who-knows-what into the radiator fans and who-knows-where else. The 997 and 40AE have vents that direct air outwards, so that's what I did. The problem was that I bent the vent tabs outwards, into the wheel well. I had a rude surprise when I installed the liners and the wheel, and realized that the clearance is very tight! The tire hit the tabs. Ugh. Doh. All that. So then. On to wheel well vents V.2 I bought another pair of liners, laid out vent cutouts, and this time bent them inwards towards the radiator fans. I'm pleased with the result. I took the car for a run which included a brief high speed section, and the front end did not get that floaty feel. It was too short to be a definitive result but I am encouraged. With the car hot and the fans running I could feel air coming through the newly cut vents. But there was still more air coming out the bottom. I plan to work on that area next but I want to wait until I can test in warm weather, which it definitely ain't where I am. Radiator frame and fan shroud showing the chunk I cut out The two pieces together showing the resulting hole into the wheel well I laid out the vent cutouts on the radiator side of the liner Head-on shot of the finished product -- what the tire sees View from the side showing how the air should be directed outwards

Quotes source post: 19244582

Doesn't really work like that. The flows in the wheel well area are dictated much more by pressure gradients and turbulence than anything else. The guided vents make a minimal amount of aero difference vs just having holes in the liner; like you said, the "tire view" is good to prevent rocks and such from hitting the cooling stack. If you want to increase the exit flow from the rear vs the factory bottom exit, add a spat on the edge of the bumper a la later GT3's. No matter if you use a crude flap protruding from the fender liner, or a sculpted flick like an OEM solution, you're squirting air outward away from the car right before the wheel well, which lowers wheel well pressure and will aid extraction from the radiator.

Like this, perhaps? Tarett dive planes with homemade ABS wheel well deflectors and Demon Speed cup lip

I own a 996-01 Cab and have purchased new CFS radiators and a center radiator. One rather rainy afternoon, I began to scour the net and various part vendors for the mounting brackets, I came across part #11, which is the back panel ( Porsche 99657515101 ) that mounts behind the center rad which sends the center radiator airflow under the car, into the existing slots in the under pan. Since I am not going to track the car, and most of my driving consists of driving in local two-lane curvy roads from Shades of Death Road to back roads of the Poconos, although I did experience a light front end while driving at 120, I do not think that the venting wouldn't be much of a hindrance to affect my driving as most of my top speed never gets past eighty-five to ninety, to begin with. If one notices the top of the back panel, several plastic bungs slip into the #2 bracket.....although I riveted on some metal brackets to #2 bracket as there are some lower side mounts on #11 that use bolts to further fasten it. . Sometimes, I wonder just how many other obscure Porsche parts are available?,