i have a 90ls teg that i just boosted the question is if i have a 3in downpipe and a 2.5in exhaust will i lose hp also have a stock cat

 

if I were you i would just take the cat out. I would think you would if you had a stock cat.

 

you wont lose hp you just wont make quite as much. buy a high flow cat, test pipes fucking suck...

 

who ever wrote this is a jack ass......o yeah that was me. hehe I didnt read the post right. you wont lose HP But youll gain if you cut the cat off. not much

 

you want the biggest, most freeflowing, less restrictive exhaust you can possibly get. zero backpressure (or no exhaust at all) would be ideal.

 

why'd you get a 3in downpipe with a 2.5in exhaust? you're not gonna make as much HP as you could be making as you're going from a larger diameter to a smaller diameter. that's gonna cause turbulence in your exhaust. on a boosted car, you want the exhaust to exit as fast as possible. so basically you either run open downpipe at a larger size or you run equal size exhaust all the way back. you should definitely avoid running larger pipe to smaller pipe like that. more or less, you're forcing a large volume of exhaust to go thru a smaller volume of pipe, which will cause more heat and less performance. hope this helps.