Hello, i just installed a whipple 2.9 on a 2017 sierra with a 5.3. Currently running 10 psi and i feel like it isn't as fast as it should be on 10 psi. Need to get it on the dyno to confirm with numbers. The truck is 100% stock besides the whipple and a custom tune by myself. So i am thinking the exhaust might be what is restricting me right now. How much do you guys think would it gain from having a set of headers installed and a 3.5" exhaust? And what muffler would you recommend to be as quiet as possible without restricting it?

 

With doing nothing else but just headers, I'd guess at under 30hp gain.

The factory 3in exhaust is good for a lot of power, swapping to 3.5 woudln't help you any.