You're right Zippy, Their popularity on the street was actually an unintended consequence...as anyone who has had a Turbocharger knows the snail knocks so much of the DB's and exhaust pulsation and reversion out of the system ( the turbine acts like a check-valve) that you need very little in terms of actual 'muffling'.

My point was that the reverse flow design is pretty good and even a big motor like a 500" is really only 250" motors worth of airflow on a dual exhaust system. A well designed 3" low restriction system doesn't cost you very much power and when it does it's mainly at WOT and at the top of the RPM range, 95% of the time on the street it never comes into play.

I tell a lot of people that for every 10th an exhaust system is allegedly costing their performance, I can find them 3 in tweaking their carb and ignition tuning, or by swapping them to the right intake manifold