400 hp from a 997.1 C4S: What's the cheapest way?

[rlips44]

There really is some utter cr*p talked about how to get power from a naturally aspirated engine - especially regarding how much is available from bolt-on mods. I think it's about time we discussed what does and doesn't work on these engines....

The 3.8 engine in stock tune produces 93.4BHP/litre. Not stellar by today's standards but still high enough that there's not a lot of 'low-hanging fruit' to be had. Also bear in mind that most engines that do a lot better are either forced induction or (more importantly to this discussion) rev much higher. The max BHP obtainable from an engine increases dramatically with more rpm (assuming the rest of the engine is engineered with the higher rpms in mind). Unfortunately, the 997S engine cannot be revved higher - it explodes. So 93.4BHP/litre is a good result for an engine that only revs to 7300rpm.

So what can be done. Well let's address the OP's question. There are 2 ways to get 400BHP from this engine without forced induction. The first is to have the capacity increased to 4-litres plus, the other is to start with the X-51 engine (the factory 381BHP upgrade). You simply cannot get the stock 355BHP engine to 400BHP. Period.

So what works on these engines? Well sorry guys but here's the absolute truth:

1) Induction kits. These have no proven effect whatsoever apart from noise. The standard airbox is very, very good and keeps intake air temps in check very well. A BMC-F1 panel filter is good for 3-4BHP but doesn't filter as well as the paper one. Your choice.

2) Plenums. Just don't go there. There were hundreds of discussions on 6-speed over these and eventually a lot of third party dynos. Trick plenums lose power in the mid band and give no gains elsewhere. (I bought one, installed it, found a performance loss, removed it and wasted my money so I'm well-placed to comment)!!

3) Exhausts. On the 3.8, the dire-looking pressed steel headers are far better than they look. The work well at low/mid rpm and only very slightly strangle the engine at high rpms. Good quality headers will give 6-7BHP in conjunction with a full exhaust system but only over 5000rpm. You may also lose some low and mid-band torque. The stock mufflers again flow very well and replacing these alone will give little to no gain (5BHP max). The standard catalytic converters however are very restrictive and a good pair of 200-cell cats will give 15-20BHP on this engine. The best solution is a good, matched system (headers, cats, mufflers) that will give 25BHP or so. Nobody has ever (to my knowledge) got to the +40BHP claimed by certain exhaust manufacturers.

4) Re-maps. This is so hit and miss. What does a remap do? Simply, it can alter the mixture or ignition timing at different operating phases of the engine. The standard Porsche maps are designed to run 98-RON (93-PON?) fuel and fuel the engine more or less optimally for max power so there is almost nowhere to go for a stock engine (despite the claims). Blindly adding-in timing (as some generic maps do) will just cause the knock sensors to wind it out again and the whole car will run dreadfully. Unfortunately some 'tuners' just alter the throttle mapping to give the illusion of more part-throttle power - naughty! The time when re-maps DO work is with other mods. Change the hardware (e.g a full exhaust) and you have changed the engine's volumetric efficiency at certain rpms. This usually requires the ignition timing to be changed by a few degrees to work optimally at those rpms and extra power will result, but it's very unlikely to be more than single digits.

So with a stock engine, a full exhaust, custom remap and BMC filter can give +30-35BHP (crank) and this is as far as this goes without very extensive further internal and external modifications to the engine.

The X-51 engine is a different beast however. Totally different intake system, bigger throttle body, high-flow airbox, gas-flowed heads, different exhaust headers and electronics mapped to suit make this a much better platform. This engine retains the stock catalytic converters that are now more restrictive than ever and a full exhaust on this motor will give you 25-30BHP with no trouble. There's your 400+BHP.

If you want 400+ BHP with massive torque, look at 9ff (German Tuner)'s large capacity, crated engines. Expensive, but will give you the fastest 997S out there.

When all is said and done however, to get 400+ BHP is so expensive that you could have one of the better cars Porsche already makes with 400+ BHP out the box (GT3 anyone). A full exhaust, remap and BMC filter combination however, is sensible money and makes the 997S go and sound like it should whilst giving 385-390BHP on a good engine. This would be my preferred route.

Precisely what I had done at Farnbacher-Loles, with the results as mentioned above. According to the dyno (MULTIPLE runs, temperature and density corrected) my car produced 357 hp as delivered (on 93 gas), when we were done, we had 393 (on 93) gas. Replace entire intake, air box, and exhaust system from headers to tips as well as custom software for the mods. The car drives perfectly at all rpms and throttle positions.

I recently drove the 997S-2 on the track at Porsche driving school, my car feels about the same, but sounds better. Total cost for me was 10k, which, in comparison to the Factory X51, was worth it to me at the time. Today, I would just order up a 997S-2. I drove it on the track with PDK, if you are tracking the car, that's the way to go. For every day use, I enjoy moving the gear selector and clutch, even though it is slower. It's just fun to me.

BTW, I have a perfect, stock 997S exhaust with the stainless steel tip option, 2300 miles. If anyone is interested, please pm me.

Next car will be the 2011 GT3.....