I have a G35 sedan and I have this huge pre muffler about half way back in the exhaust. I don't know what it is for or how restrictive it might be. I was wondering any other Nissan's with the 3.5L engine (maxima's altima's) have this extra muffler as well. If so, has anyone removed it and replaced it with a straight pipe and what type of HP gain there might be. Thanks for the info.

 

catalytic converter or resonator

 

I'm assuming you're talking about the resonator and yes the Maxima does have one. I don't know what kind of gains you would see with its replacement, but I believe they would be unnoticable. People who remove the resonantor typically do it more for a deeper exhaust note than anything else.

 

I think you mean a resonator. It reduces a noise level. If you replace is with a straight pipe, your car will get much louder. You can replace it with a high flow resonator, but you will not see dramatic gains.

 

I agree that you are referring to the resonator, and that it's function is noise reduction and not worth replacing with doing the rest of your exhaust system.