If you look at this posting by @
Shiv@Openflash
http://www.ft86club.com/forums/showp...73&postcount=1
you will see the two distinct peaks on either side of the torque dip. I have a strong suspicion that is it because of the unequal length header working. Equal length headers both tune at the same engine speed but unequal length headers should tune at two different engine speed. The side with shorter tube will tune at higher engine speed (4500rpm?) and the long one tunes at lower speeds (2400rpm?)
What he had done is create more overlap by moving the exhaust closer to intake or retarding the exhaust timing and maybe increasing intake advance and this maximises scavenging at the cost of HC emissions and possibly intake noise. The loud HONK you hear when the engine hits 4K rpm is due to this effect where intake valve is opened so early that combustion gases gush into it at the same time they are escaping through the exhaust. The more the overlap, the louder the noise and OEMs limit the NVH beyond a point. We love the HONK so we can do what we want with the timings
