I've used both types and sizes of headers on a engine dyno test, first set was a set of Hooker 1 7/8 fenderwells with 42 inch long primarys and 3.5 collectors, the second set was a custom set made by the dyno operator which ended up with 2 1/4 inch priamrys 25 inches long with a four inch collector. The motor was a 426 C.I. 9.5 to 1 compression ratio Max Wedge pump gas motor, the bigger pipes made more HP and torque from 4000 RPM up On your deal the bigger pipes will really help The first blower motor I assembled and dyno tested was a all aluminum KB 499 C.I. street Hemi with a 10.71 BDS blower and Fel Pro EFI, the headers where custom made for the car with 2 1/4 primarys, four inch collectrs and a full four inch exhaust with a H pipe and s set of Flow Masters on it That motor made 1300 +HP at 7300 RPM on the dyno Your pipes have some room to allow engine power growth