Stock air box vs. K+N CAI

I just recently picked up the 2000 996 shown on the left, there are a few issues (IMSB is not one of them, thankfully) While searching codes P0154, and P1119, I saw a common thing, that is the K+N cai. The PO did keep, and give me the original air box, I think I'll swap it back in. I'm thinking the K+N flows more air, but at a lower velocity, thus messing with the expected values from the MAF. Any thoughts? Thanks, Greg

There are many, many threads about that here. Most would suggest that you re-install the original air box . Your car, your choice. But I would read the threads. And congratulations!

^^^+1

Original or 997.1 air-box only anything else is a compromise.

All I can say is that I was in exact same boat. PO just installed before selling to me, I got codes, cleared them and they kept coming back every few weeks, so I went back to stock and have never had a code in 2 years. Sold the K&N kit to 808Bill and he has had no issues. Can't explain it why it works for him and not me--definitely odd for sure.

You can certainly swap them and see the differences, easy job. You'll likely gain a few hp and lose a few codes.

I have the stock air box, and am convinced that re-installing it is a good idea. I need this to run without codes so I can pass emissions here. Thanks, Greg

When I purchased my 996, it came with a new K&N cold air kit uninstalled. So I installed it and got one code, cleared the code and it never came back. I like the look and sound of it compared to the original, and it has a sheet metal box/shroud that isolates the conical air filter from the rest of the engine compartment and vents directly to the original cold air snorkel. I dig it and its not causing me any problems, so I'm keeping it!

One key to a MAF functioning correctly is laminar flow across it,, I would not be a bit surprised if the root of the problem is the positioning of the sensor and the overall install of the Filter. Hot wire MAF sensors don't like buffeting air, its why many applications have a honeycomb air director before them in the intake. The more tube in front of the MAF the better (to a point) And avoiding anything that would cause the air to tumble .. If the oiling is uneven on a K&N it can do some weird stuff. I switched out a Hilllborn K&N setup to a Foam Media system and it got rid of some surging problems when the car hit cross winds.. The car pulled better a thte top end with the K&N so the owner like to run it.. Eventually changed the hood on the Sprint to go lower on the leading side and that fixed the issue, and this wasn't even a electronic system. I eventually figured out how to really get a good consistent coat using a cheap harbor freight paint gun to apply the oil. And run a over filter sock so I could pull it off between heats and put a clean one on to easily get rid of the mud that would build up. (Remember this K&N was 30" long, 14 wide and 14 high.. It covered the whole system. )

My 996 came with an Evolution Motorsports air box. Never any codes. Air box includes a snorkle so it pulls in outside air just like a stock box. Dry air filter cone so it doesn't get oil on the MAF. I like the looks and sounds and it probably adds a few hp. Had a k&n on my 968 with the modified air box and it was great, esp since the air box forced in outside air thru velocity stacks. Have an AES cold air intake on my Tacoma with a Green filter and love it. It also has a forced air intake. But I've read not good things about the k&n with the 996. I think it the lack of forced air so it pulls hot air from the engine compartment, thus robbing hp and seems to throw error codes. YMMV.

Over oiling is the biggest issue fouling MAF's..

Dundon tested air temp and HP with and without cold airbox. We got better performance with stock. We found that more engine heat was sucked in with cold air kits....in my case we measured 20F higher air temp for "cold" air kit....

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I believe it. My new motor will go back to stock (not quite) 3.8 upgraded airbox if I can find one.

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Definitely the way to go. Totally agree

If you want a choppy idle, MAF readings that are improper at idle, and hotter air inlet temperatures, go ahead and buy an aftermarket system. Last week we made 480HP with a bone stock 3.8L OEM airbox. #FACT

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Yep....997 airboxes are the way to go....that is what we found too.

OK, I'm convinced, after I clean up the stock box (covered in Arizona dust) and make sure I have all the parts, it's going back in. Is it even worth it to try and sell the K+N? I presume nobody here wants it, maybe ebay.

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Some people like 'em so give it a shot....

Re-installed the stock box today, luckily the PO saved all the correct hardware. Couple of things don't add up though, first, there is a small port on the rubber boot before the throttle body (see red arrow) I don't know here that goes to. Next, the MAF appears to plug in backwards, (see red circle) seems as though the PO put in the cheapest one he could find on Rockauto, time for an upgrade? Bosch good to go?

It can be helpful to give your year and model when asking for tech support. My '99 intake boot is different than your pic so I would just be guessing. As far as your MAF sensor plug being backwards, it was discussed a couple of days age here . Good luck!

I think you have a Tiptronic airbox, as those have that little port by the throttle body. Is your car a Tiptronic?

Car is not a tiptronic, and the air box came with the car, along with the stock springs and various bits. I've plugged the tube for now (forever?) Thanks, Greg

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Idaho is right, the 2002 and up Tiptronics are the only ones with that extra port, it goes to a venturii to help the Power Brake Booster during low manifold vacuum event. It must not do a lot of good even for the Tips, because Fabspeed plugs it off also on their CAI kits. So your Original air box/hose is somewhere else..

Someone probably got tired of buying the Bosch MAF only to have it fail. That's due to being covered in oil, and fouled from the open element air filter, and the oil they treated it with. There's NOTHING good that come from these intakes. I am not saying this because I am a purist, I am saying it because I have 18 years of direct experience proving they are inferior to a stock airbox.

Drove it for 50 miles last night, and codes came back. Frustrating. So, plan going forward, is replace upstream O2 sensors (again, looks like all 4 are the same, cheapest available) with Bosch units, and replace MAF sensor, then I can establish a baseline with new parts. I'll report back next weekend with results. Thanks everyone for helping me understand this car, Greg.

Am I the only one, who's never "oiled" a K&N or any other fabric type filter before?

I never oiled the one that came on my 2003 Mini Cooper S when I bought it used. By the way, if one is after a better engine sound, resonator or red cap mod can be done with the stock airbox and filter. And reversible. Sounds great at open throttle. Sounds a tiny bit better on a Boxster S, but still worth it on the 996.

My .02... I have a 2001 996 C2 Cab with approx 87,000 miles on it. I purchased it about a year ago and one of the first mods I did was to install the IPD Competition plenum, 82mm GT3 throttle body and a K&N CAI. I also got a tune installed and swapped the exhaust for a complete Top Gear system including the 200 cell sport cat x-pipe. I also replaced the original MAF sensor and the O2 sensors both pre and post cat. Very happy with the sound, especially from 5K to 7K rpm, but I felt like I lost some low end torque and smoothness as the engine winds up. So today I re-installed the stock air box, but with the silicone tube (air box to TB) and rubber cap (to block off the air box muffler) from IPD, along with a new BMC air filter. Took it for about an 80 mile drive over a mix of expressways and two lane roads and I gotta say that overall the stock airbox with the above mods is superior to the K&N set up. Smoother response, no hesitation on the way up and still sounds awesome at WOT. No discernible change in the butt dyno IMHO. I ended up wrestling with the new silicone air pipe a lot more than I expected since it is very stiff and frankly seemed a bit too long, but I was able to get everything seated and tight. So I guess I now have a K&N CAI to put on ebay...

People are fooled all the time by this. There's nothing "cold air" about it, you still induct engine bay temperature air, or even hotter air than stock. I have collected that data with stand alone dataloggers, starting back in 2008. Sometimes on a dyno the aftermarket systems will make more power... That's because of how the tests are performed, and the environment of most test cells. So the next guy can install a handicap onto his engine. When we remove them, I blow them up.

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That tube is for Automatic transmission OR X51 manual engines. Yours is a 2000, so couldn't be X51. The PO must have purchased the intake second hand and not realized it was for an auto. I would just buy the smooth intake elbow and get rid of that piece all together. It won't throw a code and will sound a lot better by cutting off the air muffler. It's a cheap part. Can find it here

FWIW, my 2000 C4 Cab came w/a K&N "dry" air filter in it. It has not caused me any problems and I would not expect it to since it is "dry" (not oiled). Looked around the Net and have not been able to find it mentioned anywhere. Don't know or really care if it makes any difference performance wise (doubt that it does) but as long as it doesn't cause me any problems, there's no way I'm going to bother replacing it w/the OEM air filter (which I'm sure will cost me more $ than it's worth). Will post a pic of it if/when I get a chance.

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I saw a few selling for under $400 and free shipping on eBay. Two questions concerning the 3.8 air box: Does it use the same air filter as the 3.6? Looking it up online it seems to. When looking for a used one, are there concerns of whether it came from a car with a manual or tip? Thanks, John

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Not so much the air filter box, but there is a difference on the intake pipe. Tip models have an extra vacuum connector on the intake hose. Manuals don't have that.

Same filter.

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Great so one less expense if you already have a newer filter for the original stock air box. Understood, so if you have a manual you could use an air box from either type I am assuming. Thanks for the responses!

If you have a manual and get a tip intake hose, you have to plug that hole.

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It's not the airbox that is different, it's the pipe going from the airbox to the throttle body. You can buy a smooth version of that pipe from a ton of different vendors for less than $100. So use the box that your previous owner supplied and just purchase the aftermarket smooth pipe that connects the box to the throttle body. or just buy a new elbow on ebay: https://www.ebay.com/itm/intake-air-...YAAOSwTuRdg0ry

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got a vid of that?

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That link looks like it�s to a stock 3.4 hose but I understand what you are saying. I thought the design of the air box itself made the 3.8 superior to the 3.6 but if it�s just the hose then that will save a lot of money. After looking at a few different threads the snorkel for the 997 air box does look like it allows for a larger volume or air to the box compared to the snorkel for the 996.

Are the 997 airboxes easier to R&R? Taking the 996s out is kind of a pain. I have the silicone elbow as well and it would be nice to not have to wrestle it so much.

The interior volume of the 3.8 box is different than the 3.4/3.6 box. I don’t have pics of the two, but should throw some up here when I get a chance next week. Plus the 3.8 box looks nicer than the finned earlier ones. I wrestle with either airbox.

Hmm, the airbox in my 99 996 has maybe one or two bolts and isn�t really hard to add or remove.

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I have the 3.6 airbox and it doesn't seem any different than removing the stock one. It uses the same mounting points and I never considered it a big deal to remove.

Have a little patience if you're trying to find a 3.8L airbox on eBay. And search via both part number and description. Picked one up a few months ago for my ongoing build for $213 and change (including shipping).

K&N is one of the best advertising companies ever. They totally solve a problem that doesn�t exist while creating problems that didn�t exist. And they make a big profit doing it. Air filtration is a simple mechanical process of catching particles. The air filter area and media determine the flow potential. The engine tells you how much air you need. Pick a good filter media, and size your filter accordingly. This is what all OEMs do really well. K&N sells you a filter with much less area but flows a bit more... This automatically tells you it allows more dirt into your engine. It has to. They tell you to oil it to catch more dirt, but OEMs stopped using oil bath filters in the 50s. They tell you it�ll filter better as it gets dirty too.... gee thanks. I did a long article on air filters long ago with a very simple test. It�s still on the web. It�s all still true. Don�t believe this? Get a K&N run it for 5,000 miles with fresh oil get a UOA check the silica. Repeat with the stock airbox and fresh oil with an OEM filter. I dare ya. Silica will go down. For the record, K&N used to call and harass me and had some advertising call center flunkie even threaten to sue me. I was a sailor at the time, so I replied like a pissed off sailor. If anyone wants to send me a crappy K&N filter for my Chevy Colorado Z71 with 3.6 V6, I will do the test myself. 12 quarts of nice oil would be good too. My P cars don�t get driven 10k miles in a short enough time. The factory airbox and filter provide more than enough filtering and airflow to meet the needs of our engines. Why waste time buying and servicing crap when you can buy a case of genuine P car filters for the same amount and save time? If you think K&N is awesome, I�ve got blinker fluid, and muffler O pipes you can buy too.

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Yup! Marketing is how most companies push products that don't solve anything. It happens around us every single day. And guess what! It works! K&N did a GREAT job at it! Made so much money off people who think the "5 HP gain" is noticeable. I fell for it! Same goes for "drilled and slotted" rotors. The 996 never needed these rotors on them from the factory. They only did it to help sell cars. Race cars have them, so putting them on passenger cars tricks people into thinking their car is a race car. Forget the fact that 99.9% of the cars will never be driven to actually use them. I know it's rare, but how many times have we heard someone brag about how much more HP they have or someone who loves to run down the list of their mods. K&N is just one company to profit handsomely off those people. Kudos to them! "Horsepower sells cars" and aftermarket parts!

I partially agree,, at "normal" engine performance levels the difference from a K&N or really any other filter is mice nuts.. However,, a 406 sprint motor on methanol with Hillborn injection at 15:1+ compression... But we are talking about a air filter that is almost as big as the engine.. Paper system vs K&N vs ITG the K&N out powered the ITG on the engine dyno at the flywheel by about 8 HP,, but the Foam ITG was SOOO much easier to maintain. Does 8HP matter when your moving north of 800.. Not so much IMHO.. the K&N didn't muffle the intake as much,, so sound-wise it won.

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If the filter is a restriction you get a bigger filter. 800 hp 9k rpm small blocks run just fine on Wix paper.

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I'm in the market for a stock 3.8 box. If you happen to come across one in the next few months please let me know

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Maybe you have the wrong size elbow for you 82mm throttle body?

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Hey Bill, yeah I was thinking that might be the problem... I have a 2001 996 with a 3.4 and perhaps the elbow was intended for another year/engine. Was looking at the model-specific one on FSI's website and am considering that one since the air box is sitting up a little bit even though it is bolted in... I may try trimming this one down to match the stock elbow first. I also tried installing the stock elbow (with the orange cap mod) but wasn't able to get it to stretch onto the 82mm TB. Thanks for the suggestion!

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Placing the end of the stock elbow in hot water may help stretch it on to the TB.

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not only that^^^, but it frees up a lot of space back there

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no, ....the nylon cover over the filter gets washed in the laundry occasionally

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Nope, if posted it would offend someone. We can only film the unicorn and rainbow stuff. It leaves the viewer with that warm, and fuzzy feeling they are looking for.

You Tube Here's a video on the dyno test of a 997 3.6 tiptronic that shows the "CAI" is actually an HAI "Hot Air Intake" and loses power. I had one of these on my '02 C2 and did like the sound, but replaced it with a stock intake after reading many reports about the stock intake working better.

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I could show you about 500 just like that. People never listen. Thats ok, they pay for it later "even though their's runs fine with it". Look at MAF values before and after, fuel trim before and after, and then wait for the trend data. When exposed to these cars from all over the planet, and the engines are all you do, you connect the dots. Sometimes it takes years, but the dots turn into plots.

Whats the difference between the 997 3.6 and 3.8 airboxes?

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Thanks for posting this video. Kind of neat, but I think one "flaw" is that the car should be actually moving vs just sitting standstill on a dyno. Air should be flowing around the car. That will potentially feed the intake with higher flowing air, as well as potentially keeping the engine bay temps down. However, this could open up new challenges for the mod, so who knows. With that said, thinking that any of these mods will increase power, and the increases in power actually be enough to actually feel is where there's a disconnect. Most people dont realize that as base hp increases, the amount of hp increase needs to be greater to be felt. 20 hp increase on a 4 cylinder is not the same as a 20 hp increase on a 6 cylinder. HP increases is all relative. Hoping to get power increases out of these engines will only leave the owner disappointed and less money in their bank accounts. There aren't any worthwhile bolt-on modifications for the M96 that the butt dyno will detect. Now if your main goal is just to make the car sound better, intake and exhaust mods are a good choice.

40th Steve - Reference Streather, the difference between the 3.6/M96.05 and 3.8/M97.01 boxes, other than the plate, was the 3.8 box had a vacuum resonance flap installed. Air flow-wise, I’m not sure. Both 997 boxes are more air tight (keeps intake air cooler) than the older M96 box and visually look to have more interior volume.

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Thanks, I have a 997 3.6 airbox installed so just wondered what the difference was and if there was any benefit with the 3.8 over the 3.6 one. I quite like having the correct engine size on the top of the 997 airbox but if the 3.8 lower section is an improvement could it be fitted to the 3.6 upper?

95% certain it will fit. Only change for 3.8 is a vacuum flapper valve not used by 996 engines anyway. I don’t know of any empirical data to support improvements for one over the other. I also like having the correct displacement displayed.

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until they get wet.. LOL adn on a sprint everthing gets wet .. Almost takes longer to clean the dang thing than swap the engine.

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That's why I put mine back on. It really helped to find a couple of oil leaks that I could not see with the stock box on. I now have them fixed and back to the factory box.