Trying to decide on exhaust. I will be running PPE Xcelerator and PPE airbox mod. I want to get the most horsepower out of the exhaust. I dont want it to be too loud in the cab.

3.5" Straight pipe (no cat, no muffler)
4" Straight Pipe (no cat, no muffler)
4" Aftermarket Exhaust (no cat, with a muffler)

What do you think??

you wont get HP from an exhaust.

you can gain a few extra ponies but nothing noticeable. aftermarket exhaust is mostly for looks, sound, and lower egts. i am running a 4'' turbo back and like it. wish i had a 5'' though. they just look more badass.

Magnaflow 5" inch TB SS, band clamps, no drone in cab with muff, warranty, still screams at WOT, best exhaust I have ever bought! But straight pipe is the only way with the VGT turbos jus my .02

I would upgrade to a 4" exhaust. It will help drop egt's. when you get rid of the cat converter and factory muffler.

Has anyone tried the new 6" bullydog turbo back? I bet that sounds sick.

http://www.aquasunmotorsports.com/shop/store/product_detail/328/BullyDog_6-Inch_Aluminized_Turbo-Back_Exhaust_182061

Its only for Cummins.

Thanks for the replies guys. Looks like a 4" turboback will go on the truck soon.

4" is the way to go. We have the 4" MBRP straight piped kits ready to ship, they are the best deal going right now.

MBRP 4" Straight Piped Kit (http://performancetruckproducts.com/Diesel-Power/GM-Duramax/07.5+-LMM-Duramax/DPF-Delete/Exhaust/MBRP-4-Turbo-Back-Aluminized-Exhaust-w/-Muffler-Delete-Pipe-01-09-Duramax-2500/3500.html?keyword=s6004plm)