I am running a B16 on a stock '90 si exhaust(civic)...with the stock headers. how much of a power loss do you think I am looking at. the car really struggles to breathe around 8k. I was just wondering how much a cat back would improve performance. the car already as a cai and underdrive pulley....any thoughts? thanks

 

how old is your cat,
thats probably where your problem lies.

of course a new exhaust will benefit you over the 13 year old stock stuff.

 

I doubt its the cat. My money is on the exhaust. replace it with 2.5" is my recommendation. the b16 likes to breath, and 8200 rpms is moving alot of air.