I have a bone stock lg4, and I know that exhaust is the very first thing I should upgrade. If I keep my stock manifold, and replace everything else will I get more power, or is the manifolds the main restriction? This shop is giving me a killer deal. 300 for two borla mufflers and dual exhaust with a x pipe from the manifolds back. I just want to hold off on headers until I do my head swap.

 

u ll gain horses for shure...stock pipe from the cat convertor back is 2 inches which is amazing small...u need 3 inch pipe to make it flow desent

 

So what would be a good diameter piping for the dual exhaust setup? As for as smog regulations go, to pass the sniffer would I have to run dual cats?

 

ow i dont know about the smog...i live in medford oregon so here if a car is 21 year old u dont have to pass smog...i have 2 on the left exshaust system...3 inch pipe from where use to be the cat convertor to the mufler and then 2 pipes by 2 and half inch...and that is orginal stock exhaust system from 4th gen z28 whit 2 cat convertors,so i guess u wont have truble passing....i think as long as u keep the cat convertor u ll be fine