Routy wrote on 12/08/09 at 06:08:52:What I don't understand is why we worry about these bikes, that might have a slight filter restriction (nothing proven that I see). Because if it really does have a restriction, it would only be occuring at WOT. So if its a little restricted at full throttle, what do we suppose the restriction is at less than 1/2 throttle (65mph?),....or even 3/4 throttle ? If you think there is any restriction at 1/2 throttle, what do you think would happen at WOT ? I would sure think it would be running very very rich even before changing to larger jets. I detect no signs of running rich at WOT.
There is some degree of drag in all airboxes, filters and exhaust systems at all engine speeds. Aerodynamic drag is proven and easy to measure in a lab.. there is nothing left to
prove, except that the drag is significant and detrimental to the performance of our bikes.
You are right in thinking that the drag is most pronounced at WOT (and maximum RPM) and goes unnoticed at most common engine speeds, but the drag is not like a switch that kicks in at some point. There is some restriction at idle, more at 1/2 engine speed, and most at redline. It is less of a switch and more of a nonlinear "ramping up" of drag. The restriction does not increase 1:1 with RPM. It increases with the square of RPM.. if RPM (and the resulting intake/exhaust velocity) doubles, the drag caused by all the intake obstacles and exhaust bends, baffles, etc will quadruple. That's why we don't notice much restriction at the speeds we usually ride at.. you have to really wind the engine out to notice a gain in power from one of those pod filters, open pipes, ported head, stuff like that.. and even those measures have to be balanced by richer jetting or you'll
lose power due to the mixture being too lean.
Edit: Man, that mini-pod Gort has on the crankcase breather is slick.. I'm doing that too if I ever eliminate the airbox.