Im thinking of running a full exhaust all the way to the back with a muffler on my turbo ls colorado. I know thats going to kill a lot of power but i was going to add a eletric exhaust cut out and dumb right after the down pipe only thing is that i had to use some 2 1/4 inch pipe to get the down pipe to fit. Is that going to kill a lot of power?

 

So the downpipe is only 2 1/4in pipe or the exhaust past the downpipe?

For sure a full exhaust could kill over 80-120hp depending on how much power you were making to begin with.

Sloppy mechanics did that very test on his colorado. Made like 520hp with a single 3in exhaust with 13-14psi, then opened the loud valve (cut-out) and made like 630-640hp and boost went up to 17-18psi because the restricted exhaust will lower boost levels.