Replacing Stock Exhaust with Motorsport's Exhaust

[MJSpeed]

Hey everyone, is it possible to change out the stock MY '04 GT3 exhaust for the Motorsports one. Obviously I know you'd have to remap the ECU, but if it is possible is there anything to gain as far as HP/Torque?

Is it true that the GT3 engine needs the correct amount of backpressure in order to deliver on the goods?

The way I've always known it was the less restriction the better the output, so if you could straight pipe it out wouldn't that increase performance?

[KarlS]

It can certainly be done but it may be easier and cheaper to just get an aftermarket product such as Europipe.

There are two Motorsports exhaust systesm, one for the GT3 Cup that uses cats but no mufflers and the other for the RSR that uses straight pipes. Obviously the problem with the RSR exhaust will be emissions and noise.

Even the GT3 Cup exhaust has issues. First of all, it is also pretty loud and could get you pulled over just for that.

Second, it only has fittings for 1 oxygen sensor per side, whereas the stock exhaust uses two. I suspect this will cause problems with the OBD II system but there may be a way around it.

Another problem is that the Cup car cat is a single large unit with a center exit exhaust. To mount this on a street car you would either have to use the Cup car carbon fiber bumper cap (~$3K) or hack an opening in the street car bumper just under the license plate.

You can probably make the Cup car exhaust work but you'll end up spending $6-10K for it depending on how much custom tuning to the DME is needed. After all that, I doubt you would find more than 10 HP.

As for your question about wouldn't a straight pipe be better, in theory, yes. However, not just any straight pipe will work. The size and length are critical. It is easy to actually decrease HP with exhaust mods. The Grand Am teams spend a lot of time on the dyno tuning the length and profile of their exhaust systems to maximize HP.

As I said, if you're looking to pick up a few HP, use a reputable aftermarket firm that has already done the design and dyno testing. Just make sure they offer a money back guarantee and make sure you do before/after dyno runs to confirm their claims. There are a lot of products on the market that will actually decrease HP, so buyer beware.

Karl