i put a custom exhaust on my 87 na and i was wondering what the HP gains were... 2.5 DP, no pre cats, straight through brand new main cat, 2.25 pipe to a single straight through muffler. (and i can shoot flames now!!! hell yea!!!

 

Prolly like a 25-30 hp gain.. It's basically a full straight through exhaust

 

If it still has the stock main cat, I don't think he is going to see a 25 horsepower gain.

 

is the brand new cat an oem replacement or a performance

 

Oh, a FUNCTIONAL cat... well then prolly 15hp. Get a staright pipe and swap in a real cat everytime you have to get emmissions checked

 

performance cat

 

then maybe i would say 20 then... ditch the cat but have something put in(like said above) if u have emmisions!