I wont comment on the primary length issue or the any of the other technical blurb. What they are saying is that a smaller primary coupled to the stepped collector tube will increase the exiting exhaust speed. That in turn with some trickery on the valve timing will net an increase in power by partly pulling the intake charge before slamming the exhaust valve shut which causes a ramming effect. I think....... Bottom line is the stepped exhaust system is on all the top race cars now nascar,F1 and bikes etc.
Edit this is a head spin on the subject
http://www.performanceforums.com/for...-67265439.html
Bob