Does anybody make a Performance exhaust system for the 04-05 GXP ?

You could change the cat and mufflers. As far as a complete drop in exhaust kit, nope. No one make aftermarket kits for the Bonne.

the GXP does not have a res about all you can do is a high flow cat and different mufflers

Both of which will likely provide minimal gains for the GXP. The exhaust flows pretty freely as it is.

Then again, that'* not to say it wouldn't be louder with different mufflers, if exhaust noise is what you're looking for.

No gains whatsoever. The stock exhaust is tuned one. So unless it rusted off, or you want it to rumble louder, your throwing your money away.

x2


even for the noise, i personally LOVE my stock system

I do love the sound of it, but I would not mind it being a little bit louder. Sounds great from the outside, but I spend most of my driving time on the inside.

I was hoping to get a couple extra ponies out of it and a little louder rumble wouldn't be all bad either.

Anyone ever looked at the STS Corsa system? Is it even close?

If the inlet on the muffler is the same you could just use that and then weld it to the stock pipes as long as the muffler will fit into the current spot on the Bonne. You will not find a complete aftermarket kit that will just clamp, bolt-on, etc to the Bonneville. The H-body wasn't exactly given much love.