Tuning exhaust performance is very complex.
The cam profile, especially overlap and cam timing, can affect exhaust systems. I imagine most of us that have modified our engines with larger valves, porting and polishing, cam, header, and larger exhaust pipe, free flow mufflers, don’t really understand what changes have occurred to flow and volumetric efficiency, and what affects those changes make in the ultimate desire for increase power.
Are the headers we buy equal length? What lengths are best for a 22R and 22RE? Why does a tri-Y design scavenge better? Does it scavenge better at WOT or partial throttle? I believe exhaust tuning has been historically trial and error. Is the testing done at WOT or a range of RPMs? There are physical “things” going on that may not be easily measured or even calculated. Can you measure swirl on a flow bench? Can you measure the pulses at each tube and at the collector? Can you measure the sonic wave caused by exhaust pulses? Can you measure the mass flow at WOT (wide open throttle)? What affect does increased compression cause? How about the number of angles and cut degrees on the exhaust valve? How about the AF mixture – wave velocity changes depending upon a lean or rich mixture.
The size of the exhaust tuning from the collector back can be critical to maintaining the performance gained by the header and the cam. Is the tubing mandrel or crimp bent? Does a 2.0” diameter flow better than a 2.5”?
Lots to think about and more that I will most likely never completely understand.
Gnarls.
