is a 2'' ID header collector to small for a b16a2 engine with intake ecu and exhaust mods??

 

i would say so... you should go 2 1/4 or 2 1/2

 

2.5 will make more power at high end but how this will feel at low end rpm?

 

At lower RPM there will be very little noticeable difference on a b16 whether you are on the 2 1/4 or 2 1/5.

 

I ran full 2.5 on my old b16a hatch, it had skunk2 stage two cams. It was fine. To be completely honest they dont have much torque anyway, so i didnt notice much of a difference from the stock exhaust on the low end, but she would scream at high rpms.