I have B16A head/B20B block. I want to move my peak torque to higher rpms and also hold the peak torque longer (right now probably around 4500 rpms peak). I'm wondering if by increasing the pipe size of my catback from 2" become 2.5" will help. But my primary collector now is only 2" (4-2-1 header). My engine is lightly modified and not yet ported and polished (but thinking to do it soon). Thanks.