In exhaust tuning it is well established that a 4-1 header provides the greatest Hp but only at peak rpm. For a more street efficient system a 4-2-1 give more gain at low rpm and moderates the peaks. Conventional design criteria says to tune the primary tubes to reinforce the rpm you want the greatest gain and run the secondaries approximatley 15 inches longer. I have started exploring that this may be incorrect. I am looking at designing the total of primary and secondary at the calculated length for the low rpm peak (long tubes supplement low end torque). Then from this package i would design the primaries only at the calculated length for the high rpm peak (shorter tubes reinforce higher rpm). I have searched in several texts and found now research on this approach. Any thoughts from my compatriots?