i bought a obx racing highflow cat now its not a actual cat its the size of a car but its straight through like a muffler even has all those little holes in side like a muffler how much power should i gain from slapin this thing on my civic i have a jdm b16a intake/header/exhaust installing cat

no dont use the cat just go straught piping all the way.......

i hear high flow cats make a difference. Not sure what kind of gains u gonna get tho. i'd say like 3-5 hp or so. exhaust will sound louder too. Dont go straight piping... save the environment!

The cat will not help all that much but it will most likely change the note of your exhaust a little. Probably about 3 hp, the best thing to do depending to what model car you have is to gut the stock cat. but if you have obd2, or a car model 96+ you will have to use the hi-flow cat to keep your check engine light from coming on.