I would like to pick up some more Mpg out of my wife's Denali. I know a cat back would help but she doesn't want the loud exhaust. Who make quiet but effective system? I like the sound of the stock and i do like that it is quiet when driving(i have a 500hp 2004 gto that i use for the noise). Would an x-pipe help with anything or is the stock system just to restrictive? I did a K&N cold air intake so i know the exhaust would work well with that. I would also like to get some tunning done. With a tune, intake, & exhaust about how much hp is that worth?

 

You start off asking about mpg then the last question is how much hp would that be worth. I say get a tune from Nelson or someone like that and then remove the stock muffler and run a long aftermarket muffler. I would think that the pipe diameter itself would be fine just the muffler would be the main restriction.

 

I agree...just replace the stock muffler with a long Magnaflow.