I'll never argue the HP issue, BUT my EVOM intake lets the intake resonate at about 4500 RPM (I think the stock design silences it). So, it has the coolest roar at that RPM on half to full throttle. Totally cool and much cheaper than an exhaust mod. Was a nice mod and an easy DIY install.

 

Sorry to break it to you but exhaust does add HP. Porsche's approach was completely different. They have to consider noise restrictions, comfort & emissions. Aftermarket manufacturers do not have to consider these things as much.

I have a full AWE system on my car and it made a big difference. Not a vast difference that a Turbo or a Supercharger would, but still was very noticeable. My car was putting down 327.5 whp on the dyno after the exhaust install. I never dynod the car before so I cannot give you the stock numbers but it is clearly below it.

 

You must not be familiar with X51 on a 997.1
I'm no expert, but didn't HP go up from 355 to 381 with mods like intake, headers, tune (?), and a few other items? If you do an intake, and the headers, but swap those other X51 things with 200 cell cats and a 93 Octane tune, I would think that 381 is within reason.

 

My take on "why Porsche doesn't do it in the first place?". Because they know where to go for the 10-15 hp incremental gains for the next model year, etc and are saving them. Tuners just expose those gains for the current model year. Just a theory.

J

 

I am aware of the X51 package - as I understand it, the factory kit includes modified heads and costs something north of $10K - at that price point, FI starts to look like a lot more power for the bucks. I bought my C4S used and it came with a Techart muffler - the sound is gorgeous, but I doubt that it adds any power. Although I believe that small (5 - 7 %) improvements in power may be available with the right combination of intake, exhaust, and reprogramming, I have yet to see documented, verified, and controlled before and after dyno results to prove this. This is not to say that it's not possible, just that there seem to be a lot more claims than proof. As noted on this thread, several (many?) people have documented no increased power through their bolt on mods. Having said all that, sound, looks, and weight reduction are true benefits from many of these mods that are easily verifiable and may very well be worth the cost to the people performing these mods. It still looks to me that any significant (10% + power increase) will have to come from FI or major internal mods - cams, compression, heads, etc.

As stated before, just my opinion - and I would love to be proved wrong.

 

X51 has mod'd heads for more air/fuel flow, increased valve spring rate and I believe different valves for a higher rpm redline...this give much more air flow hence a different ecu tune.

 

Mike the heads on the X51 is not worth that much hp, keep in mind that the OEM car makes 93hp/litre (997.1S) with the OEM heads at under 7k rpm, which means the non X51 heads are good as is. Most of the hp gain is from the larger cross section of the intake manifold, larger throttle body and dual snorkel setup to feed the air it needs. You could build an X51 "lite" without the heads and get 95% of the performance increase without spending a boat load for heads that have just a basic cleanup with a stiffer exhaust valve to raise rpm by just 150rpm. Just an FYI, the X51 heads uses the stock cams as well as valves.

Dave