Im still sort of new when it comes to V8s so please forgive me. I have a 4.8l with gibson headers, highflow cats and stock muffler/resonator. If I take the stock muffler off all together at the bolts past the cats is that going to hurt my mpg? I know its going to be loud as hell and probably get me more hp, but im worried that because of no tune for it that it'll kill my mpg.

 

I doubt you would notice besides the sound.

 

Will be loud for sure. I can tell you, you'll lose low-end power, 4.8 likes to rev and lacks torque. If you do alot of city-stop and go driving, you may lose some mpg. I doubt it would be much either way.

Tune won't matter for removing muffler, you might pick up SOME power higher in the higher rpm's. Again, probably won't be much either way.

I think you'd be better off getting a single in/out straight thru muffler design personally.

 

Do not just cut off the muffler, you will hate it. There is some great information about exhaust setups in the Stickys section at the top of this Section. Particularly, the 'exhaust backpressure myth' one.

 

Oh I wont be cutting it off directly, just unbolting it. The original muffler is huge and just doesn't belong on there. The rest of the exhaust is cut 6" away from the muffler and everywhere wants to charge me for a full kit when i want to keep it clean with no tips sticking out the side or back. So I figure screw it and take it off to see what happens. But I heard that it can suck your gas right out cause of back pressure and no tune???

 

Like L33Z71 said you most likely wont lose any mpg's unless you do a lot of stop and go/city driving. As far as HP increases...dont get your hopes up. Countless people have made 1/4 mile passes with full exhaust vs. open exhaust via a cutout and showed no noticeable gains. Same as on a dyno...maybe a tiny increase in the 4k+ rpm range and nothing down low. So if you just want it loud, id suggest a cutout.

 

Gotcha, but then what's the point of buying an exhaust? If there is no gain with it being open then why spend $200+ on a "perfomance" one???

 

There isn't one, if you just want to be loud. An open pipe driving around will honestly sound like crap. Just keep the stock stuff on there and get a cutout so you can at least tone it down when it gets annoying. An aftermarket muffler such as a magnaflow will out perform the stock muffler by quite a bit, but going from stock to straight pipes you're not gaining anything, you'll lose low end torque that the 4.8 already doesn't have much of and it will sound like trash.

 

Gotcha, thanks for the insight guys

 

I drove around with my muffler cut off and dumped for almost two years. Let the cats do the noise. I liked it for what it was and wasn't stupid loud. But nothing beats long tubes with a Corsa