I wonder, what is the efficiency our the stock intake/exhaust systems on our bikes. In other words, for a 790cc engine, with the stock cam/valve setup, are we actually pulling in 790cc of air at ambient pressure with every intake stoke? Probably not. I'm guessing the efficiency is around 70 or 80 percent, but I may be way off. I suppose it wouldn't be too difficult to hook up an air flow meter to the opening on top of the airbox. It would take a little more ingenuity with the airbox removed. You could measure air volume against rpms and get an idea of the cylinder efficiency. I wonder if you could get over 100 percent with a turbo system.
A lot of things affect the intake, like air friction, air turbulence, and pressure drops throughout the system. I have heard of a thing called scavenging, which is where the exhaust pulse bounces back from the end of the pipe. It hits the exhaust valve as it opens causing a slight vacuum to help evacuate more exhaust from the cylinder. That allows a bit more air mix to enter on the intake stroke, and thus more power. Scavenging depends on the shape and the length of the exhaust pipe, and then it only works in a narrow rpm band. It would be like tuning a trombone. You have to get the length just right for the travel and timing of the pulses to work right.
It would be fun to have a well stocked garage with a dyno and an exhaust gas meter and air flow meters to experiment and tune our bikes to the max. Unfortunately, most of us don't have those things. All we can do is make informed guesses and hope we don't screw things up too badly.
Cody
