Just a quick question but i have been offered a JDM itr 4-1 header with the 2.5 collector for my B20-vtec (should liberate some more horses than this ebay 4-2-1 with a 2 inch collector)

looking on the B20 thread it seems some people have had pretty good results with this header, though when i last had one fitted to a B16a it really killed the bottom end torque and hp, will it do the same on a b20?

Its pretty much a stock B20z1 block with b16a head with a skunk2 pro intake manifold/ spoon throttle body, the rest of the exhaust system is 2.5 (jsut not the header).
The other manifold i have been offered is an older Comptech 4-2-1 with a 2.25 collector

i cant afford a tri-y as i have to ship one form the states and im going to get *** raped by customs with 27% tax on it (makes a $300 copy header near £350 with shipping and duty). plus i want to buy and fit my 99 spec ITR cams to (it only made 185 fly wheel hp and 147 lb/ft on the dyno dynamics after mapping as it was)

also will an ITR header fit snugly under my B20 block with a b18c6 oil pan?

thnaks!