Back pressure does not mean the pressure in the exhaust has a backwards direction. Pressure is not a vector, it has no direction. A pressure wave has direction, and as the video describes, the wave flows out from the cylinder head thru the exhaust, and bounces back on any change in flow restriction.
I think the term is referring to the back-side of the engine, the exhaust pressure (vs the intake pressure).
something that is equally important, I have read about mods on several bikes where someone took the stock air box and filter off, and put one of those shorty little air filters right on the carb intake. Dyno tests indicate that even with rejetting, the bike lost HP. It looks cool, but its not functional. When I see a Honda 750/4 or another vintage bike set up like that, I cringe.
Last edited by KCW; 05-22-2018 at 09:05 AM.