I have a jdm b16a, installed vibrant 4-1 header on, that was the only thing missing since I have a cat back exhaust. After installing the header, I did feel a dron on low end torque, but felt no gains in the high end, my car rev's up to 8800 rpm, & felt no extra power there?

BTW, the stock exhaust manifold has the 2 o2 sensors just by the engine block, the new one has 1 on the bottom end of the headers. I installed the other one after the cat, now my air fuel meter goes crazy occasionally ...

 

well, *** dyno is not a real good way to sense power, as far as the 2 o2's that you have; your supposed to splice them together if your goin to use 1