There has been considerable debate concerning the gains with a cat-back
exhaust system. I've always thought that the stock exhaust was pretty good
up to around 6000, but would choke the car above that, and that an
aftermarket exhaust would show the greatest gain up high in the rpm band..
Well, I was wrong!
Yesterday, I took my car to AWE and had the latest Techtonics Tuning
stainless steel exhaust system installed. This system consists of two
resonators, a Borla muffler, and heavy-gauge 2-1/2" piping. Fit and finish
is excellent. My car has Schrick 268 cams, a Schrick VGi manifold, Garrett
11c chip, and the standard airbox mods (cone and snow-screen removed).
My car was dyno'd immediately before and after the exhaust installation. The
results with the exhaust:
* +9 hp at the wheels at 6000 rpm.
* +13 ft-lbs of torque at the wheels at 3500 rpm!
This is obviously quite a bit more than the "5-6 hp" that is so often bandied
about when people talk about exhaust systems. Now I cannot say if the
results with a "stock" engine (without the cams and manifold) would be
similar, but on my car, I'd say the gain is "signfigant"..:-)
With a 1.15 wheel-to-crank correction factor:
Stock Exhaust TT Exhaust Difference
191.6 hp @ 6000 201.8 hp @ 6000 +10.2 hp
184.6 ft-lb @ 3500 199.3 ft-lb @ 3500 +14.7 ft-lb
Some pictures of the exhaust and the dyno plots:
PS: It sounds GREAT outside the car. But I haven't had it long enough to
make real comments regarding the liveability of the noise level inside the
car (a factor to which I'm rather sensitive). Give me a few weeks! :-)