The size of the primary tubes actually will impact the power range of the motor, as will the length of the collector. The 1 3/4 tubes will have a slightly higher torque range than the 1 5/8 tubes. I think Hi Perf Pont did an article on this last year. I went with the Hooker comp headers, they are 16 gauge vs 18 for the hedman. Although the hooker headers will hang a little lower than hedman.