Porsche 996 Fast Road / Track Day Car - Oversize Build

As I take a lot of info from this place I though I would share some info on my car & a recent engine (re)build that may be of interest. The car is a late 996.1 factory aero-kit, non-sunroof C2, bought as a project to upgrade and use. The aim was to sympathetically upgrade into a fast road / track car using a clubsport mentality keeping it looking as standard as possible, while improving reliability, drive to the circuit, drive home – Where possible all upgrades would come from within the Porsche food chain, GT3 / RS / Cup, using genuine Porsche parts. Buying a 996.1 GT3 was an option, but due to its initial cost, appreciating nature and rarity it would have just sat in the garage next to the other cars that I rarely drive. – I wanted something that I could use and enjoy without worrying about mileage, stone chips, modifying from standard etc etc. – This was to be as much about the journey as the destination. I have been running the car for circa 2 years with a standard engine, albeit with LTT, centre rad, FVD X51 sump and the upgrades listed below, should anyone require any details on anything ask, however for the time being I will focus on the recently rebuilt engine. Oversizing the M96 is becoming more popular but there is not a huge amount of info out there. 996.1 3.4 going to a 3.7. – Proactive upgrade as oppose to a failure. – I wanted a little more performance, and once the maths were complete, this made most sense to me, given where the car was and what else I could have gotten into. Expectations, management of.., As touched upon there is not a lot of these in circulation and as such not a lot of information on what to expect from a data/figures perspective. – In fact there is very little dyno info out there for the M96 cars in general, there is lots of speculation and assumption, but not a lot of hard fact. – Some say expect 350bhp from a 3.7 with some breathing mods, I was skeptical on this. 996 3.4 was rated at 296 bhp when factory fresh, most generally state the 300 PS number, with 256 ft/lbs of torque. – Having done a fair amount of research and spoken to both Wayne Scholfield & Charlie at Surrey Rolling Road, neither have ever seen an M96 make the quoted number, ever. Mezgers general do make their numbers, M96 are always below. – The question is, how far below, data on this is thin on the ground, and given the cars are also circa 20 years old, wear would also contribute to lower still numbers. As I needed a datum, ever the optimist in my mind I decided that my car would have produced 296 bhp and that over 18 years it will have only lost 5%, so the fictional output number I started with for mine was a 281.2 bhp. I then stumbled upon a thread by Y2K, I hope he does not mind me sharing, he had his 996.1 dynoed at Surrey Rolling Road and was good enough to post the plot, at peak his car made 272 bhp with 250 ft/lbs, draw from this what you will, but I feel with this info and the comments from those who have a host of experience on the topic, is generally where the cars are at, and not anywhere near the much mentioned 300 number. With the above in mind, getting a 3.4 from, lets say 280, to 350, with a 300cc increase and a few bolt on breathing mods seem totally unrealistic to me, and as such helps to manage and realign expectations. The rough spec of my build was as follows, a big thanks to Hartech whom work with me, allowing me to deviate from the norm and for fitting lots of additional parts and items including some that are normally reserved for their race engines. 3.7 Closed Deck, Nikasil Liners, new forged pistons etc. Carrillo forged Rods Threaded Core Plugs Custom Additional Crank Shaft Bearing. Latest Large Porsche IMS Lightweight Flywheel & Sprung Clutch, balanced to Crank RSS Underdrive Pulley X51 Intake Manifolds X51 Runners X51 Additional Oil Scavenge Pump X51 Exhaust Manifolds 3.6 Cats FVD Motorsport Sump with X51 Baffle Secondary Air Pump Removal ECU Remap (Wayne Scholfield) The above was on top of a whole host of other upgrades and stuff, chains, seals, pumps, fuel rails etc etc etc. – In reality there was not much that wasn't changed! But none are really performance rated. Now the only other performance related issue that I will share feed back on are, the heads, plenum, throttle body, airbox and air filter. The standard 3.4 heads are CFD designed and generally flow well, polishing and light porting of the these produces very very modest gains, regardless I had them done, rebuilt and skimmed. – I was told to get more from them you need to move into the realms of adding more material to the ports and then reshaping, other stuff was also mentioned but it escapes me. I looked into X51 heads, however I believe these are, with the excepting of being skimmed, identical to the standard heads, the difference in performance comes from the cams and valve profiles, not much info out there on these, and as much as I would have liked X51 heads, the costs and availability were a bridge to far for me on this project. Plenum, I fitted an IPD competition plenum with a 997 GT3 82mm throttle body, linked to the standard airbox, with a resonator delete and BMC panel filter. – If the internet is to be believed this is a solid setup and should produce gains, this is where it got interesting. The car was dynod, the results were deemed to be sub-optimal, so various items listed above were systemically removed and replaced in various combinations and the car again dyno'd immediately after to compare the results and this is what was discovered.., IPD Plenum with 997 GT3 throttle body, reduced engine output and left flatspots and holes everywhere in the curve, apparently down to the lose of exhaust scavenging effect. Resonator delete airbox with BMC filter, produced less bhp & torque than a standard airbox with a standard filter. - The rational, in deleting the resonator the airflow is more turbulent, the MAF doesn't like this and winds things back, standard filter flows more than enough air. The optimum solution for the most bhp & torque was, standard airbox with resonator, standard air filter, standard throttle body and a 997S plenum. People may have an opinion on this, however its based on data, and as much as the larger shiny throttle body, IPD plenum etc look great and make the car sound better, on my engine they did not increase performance, they hindered it. In the end after lots of tuning, where did I end up, the engine produced 325 bhp and 290 ft/lbs of torque. – When it breaks in I may see a little more. So based on my fictional starting point of 281bhp, I gained 44 bhp. Based on Y2K's numbers, which may be more realistic, I gained 53 bhp & 40 lbs/ft of torque. Based against the factory numbers I gained 29 bhp & 34 Ibs/ft. 996.1 GT3 factory numbers are 360bhp & 272 ft/lbs – Again from the info available these numbers are accurate with most cars dynoing in the mid 350's. With the circa 50bhp gain, if the car had been producing 300 as standard, it would indeed have been circa 350, but the reality is, it doesn't and if your considering a conventional oversize, don't expect it to. Once the engine is run in I will take VBox data on circuit which I can overlay against data I already have from before the work, this to me provides real world improvement data, which is more relevant and important than bhp numbers. – As is the fact that the engine should now be more robust, not that I had any issues prior to the rebuild. As many of you know, you can get a dyno to read whatever you want it to, we all want high engine BHP numbers and things can be fudged to suit demanding clients and massage ego's, I don't really care so wanted 'real' numbers which I am prepared to share. Car weight is another where people are coy, I'm at 1285Kg, with no fuel or driver, with both, which are critical, based on half a tank its circa 1400Kg's. – I've removed around 140Kg's from what was a lightly spec'd car from factory. For context PCGB Class 1 996 3.4 Race Cars have a minimum weight requirement of 1295Kg As far as a performance summary goes, I have nothing firm at present based on the cars actual weight, and the actual weight of a standard 996.1 GT3 I would expect the Power to Weight ratio to be very similar. – Much like the bhp figures quoted by Porsche, the weight figures are generally a long way off, with most cars being significantly heavier than people think, again a fact confirmed to me by Chris at Gravity Centre. Spec. Cooling : Porsche front centre radiator, with GT2 chimney and Cup bumper vent Porsche low temp thermostat A/C modified to run with a single condenser, significantly increasing airflow to one rad. Fan override switch Transmission : 6 Speed Manual Gearbox 997 GT3 GearShift Lightweight Flywheel, dynamically balanced to the crankshaft. Sachs Performance Sprung Clutch Sachs Performance Pressure Plate Sachs release bearing Motul Gearoil Powerflex Gearbox Mount, revised design. Front Axle : JRZ Series 12 Cup Motorsport Coilover Dampers Porsche GT3 cup Monoball top mounts Porsche GT3 Cup 2 piece lower control arms Porsche GT3 Cup adjustable anti-roll bar Monoball adjustable drop links New Porsche TRW steering rack, including tie-rods and track arms Conversion to Porsche 997 Cup electric power steering pump. Rear Axle : JRZ Series 12 Cup Motorsport Coilover Dampers Porsche GT3 Cup Monoball top mounts Porsche GT3 Cup 2 piece Monoball lower control arms Porsche Cup Adjustable Rear Toe Links RSS Locking Toe Bolts Porsche GT3 Cup adjustable anti-roll bar with Powerflex Bushes Monoball adjustable drop links Alignment & Setup completed by Gravity Center. Brakes : Front : Porsche std calipers, wear sensor & anti-vibration shim delete. Giro Disc Two Piece Floating 340mm Discs Pagid RSL29 Pads Motul RBF660 High Temp Brake Fluid HEL Performance Stainless brake lines Porsche 997 GT3 Front Lower Ducts Porsche GT3 Cup Front upper brake ducts (Radiator cowls and wheel arch liners modified for airflow) Custom 2" Brake Duct from from front Bumper to inside centre of front disc. 996 GT3/Turbo 25.4mm Master Cylinder Rear : Porsche std calipers, wear sensor & anti-vibration shim delete. Giro Disc Two Piece Floating 330mm Discs Pagid RSL29 Pads Motul RBF660 High Temp Brake Fluid HEL Performance Stainless brake lines Porsche 997 GT3 Rear Ducts Wheels & Tyres : Porsche std 8" & 10" GT3 Wheels Rennline Race Wheel Studs 235 x 285 H&R 7mm Front Spacer H&R 12mm Rear Spacer Wheel Edit; Porsche Cup BBS E29 Split rims 9" Front - 245/35/18 10.5" Rear - 295/30/18 Exterior : Porsche Factory Fitted Aero Kit Non Sunroof Car (Not removed, not specified from factory) Porsche Cup Car Front Splitter ClubAutoSport Lightweight bonnet Porsche Lightweight bonnet crest Porsche Cup Car Rear Lexan Screen Rear Wiper Delete (Done Properly via Bodyshop and not a plug) Front Bumper meshed Wheel arch modification to redirect radiator airpath. Porsche Litronic Headlights with wash delete and Amberectomy Interior : Lightend Interior, using a ClubSport mentality. (Removed circa 105 Kg's) Edit: Now closer to 145Kg's Porsche Handheld Fire Extinguisher Porsche GT3 Centre Console Delete Lightweight Carpets Body Colour Centre Console Rear Seat Delete Porsche Cup Momo Steering Wheel Heigo Clubsport Rear Roll Cage Schroth Porsche 997 GT3 Harnesses (Floor mounted Crutch Strap) GT3 Replica Carbon Bucket Seats, mounted via Porsche seat rails Rennline Billet Gas Pedal Hinge Engine : Hartech 3.7 Closed Deck Build – Complete engine rebuild, virtually everything renewed or replaced (7 month build time) Hartech Capricorn Forged Pistons Hartech Capricon Nikasil Liners Carrillo Forged Rods Hartech Threaded core plugs Hartech Additional crankshaft bearing (First Road Car) Cylinder heads rebuilt, polished & skimmed Latest 2006> Porsche large IMS Bearing Porsche X51 Intake Manifolds Porsche X51 Runners Porsche X51 Exhaust Manifolds with Titanium Studs Porsche X51 Additional Oil Scavenge Pump Porsche X51 heatshields & a/c pipe work. Porsche 997 3.8S Plenum Porsche 3.6 Standard Cats Lightweight TG Stainless Steel Sports Rear Boxes (Mild sounding to pass trackday db levels) Secondary Air Pump Delete Wayne Scholfield ECU Re-map FVD Motorsport Sump, with X51 Baffle Uprated Oil Pump components, Shaft (LNE), Piston & Spring (Porsche) New Porsche Fuel rails, coolant tank, oil cooler, Water Pump, aos, Over engine brake lines, Clutch cylinder, Exhaust Hanger Brackets, all exhaust bolts are titanium for serviceability. Porsche RS Engine Mounts RSS 4" Underdrive Pulley Belt driven Power Steering Pump removed. PS-30 Powerlite LiFePo4 Lithium Ion Battery There is probably more and the journey will continue, however this is all I can remember for now - Peace :bandit:

this is absolutely excellent. will you be throwing pictures up? ive just bought a 997C2S and will be following a similar path to you.

Fascinating- thanks very much for sharing

Very interesting. The factory figure will be at the flywheel and yours will presumably be measured at the wheels, how did you get to a comparison?

A great write up Simon, thanks for taking the time to do this, very informative and some interesting findings :thumbs:

Great post.

Great post! I followed much the same course of thought and have just finished something similar with the recent Hartech upgrade of my 996.1 RPM CSR. Mine is an early car, a '98 with, as far as I know, standard internals and throttle body, with Top Gear manifold, 200 cell xpipe cat and Milltek exhaust. With the 3.7 conversion it produces 330bhp and slightly over 300lbft (I'm told the bhp figure was actually higher still at 339bhp on the tuners dyno but I don't have the print out for that, so hearsay). Technically yours should be the more powerful, I think it just goes to show how much variation there is between individual engines, slightly different mods and the actual dyno on the day.

Sounds like a great build. However i understood (by the fact that basically I've never seen anyone do it) that fitting the x51 scav pumps was not straightforward. Or is it just finding the spare parts that's hard?

I have a load of pictures, however am not as organised or committed as some whom do superb build threads, I will try and get some posted. Dammit it will be interesting to see where you and MC end up. – From what I can gather the standard 3.4 heads although optimised for a 3.4, are restrictive, you have a solution for this, amongst other things! I had hoped the IPD & larger throttle body would bring benefits, reviews are mixed but again, data isn't available, but unfortunately not, bigger isn't always better! Disappointing particular considering the cost, circa £1k! – It did however look nice next to the X51 intake manifolds. I spoke to an engine builder whom builds for historic's, Nick Mason is amongst his client list, he mentioned that in one make series where particular engine elements are controlled one of the ways they 'cheat' is via exhaust scavenging, he referred to as a mini-super charging effect when done right, the M96 seems to benefit from this and bolting on items that upset the balance can appear to have a negative effect. Maldern, the 325 is a flywheel figure, its calculated by the dyno via the wheel figure. – There are innocuous things that can negatively affect this that you would not consider, running sticky track rubber as an example. The LWFW and under drive pull do reduce parasitic loses, all be it not a great deal so more engine power is put to the road so there may be a small margin of error – The same goes for the cup electric power steering pump, however this was fitted after the engine build so any benefits are not included, again I expect them to be minor, circa 2-3 bhp perhaps. – Although some would have you believe that an under drive pulley gets you 10 bhp, I do not buy it. Rank, your bang on in regards to any given dyno on any given day, its one of the reasons I am more interested in Vbox / lap time data. – CSR 3.7 sounds nice! – Do you track it? I would have liked 200 Cell cats but couldn't risk the extra noise pushing me over trackday noise limits. Skinny, fitting the additional X51 Dual Scavenge pump is straight forward, although your right in that I could not find anyone who has retro-fitted one. You remove the existing single scavenge pump from bank 4-6, replace with the dual x51 pump and drill the cam cover to fit the suction pipe that takes the oil that pools in the front of the head under heavy braking and left hand turns and returns it to the sump. The issue is the availability of the pumps, Porsche still sell them, they are expensive, circa £2k, however upon purchase it turned out that the only batch that Porsche has access to have been manufactured wrong and run backwards! – I was fortunate enough to source a genuine Porsche item from a fellow member. – There are some aftermarket solutions, TTP oil safer, as an example, all of which are copies of the Porsche item, however the quality in execution is not great!

I haven't tracked it as yet... although that's the intention next year after I have a few other things done, it's still on standard brakes (albeit new, with braided brake hoses and high temp brake fluid) so they're next on the list. Soundwise... it's loud. It starts with a bark, rumbles, snarls then works up to a yowl as it goes through the rev range.... to be honest it's fun opening it and listening to the noise but bloody hell it's loud! (And was commented upon by Hartech so I suspect may be too much for some/most trackdays) In fact the whole car is loud, the LWFW chatters and the polybushed suspension introduces extra NVH. That said you can still listen to discussion on the radio and converse without needing to raise voices (too much).

Very interesting project/Spec and should be a great track car, if I ever decided to get another 996 I would want to go the same route but starting with a 3.6 base car.

What's interesting is that you've made an additional 50 bhp from 300cc in capacity, the X51 intake and the X51 exhaust manifold - plus some benefit from the light port and polish. That's despite running the same cams as the 3.2 litre Boxster - with cams optimised for the additional half litre of displacement I suspect you'd make a lot more. Do you mind if I ask where in the rev range you made the most power and torque?

(I also think that is a fantastic looking intake manifold, so much nicer than the stock plastic unit).

Nice job! 8) All the right bits, that's for sure. I look forward to some pictures of the finished article. :thumb:

A lot of similarities between your car/approach and mine, although so far you've obviously taken things much further than me to date with the engine (my 3.4>3.7 is still a couple of years off...) The highest praise I can give is that I'm going to be reversing my resonator delete at the weekend to see how I feel about it (you develop a reasonable unscientific "feel" for your own car over the years - this was an early "easy fix" that you've now made me question with that write up.....!)