With an approx 100 mph (assuming no baffles) wind blowing thru the cowl area how much time does that air have to heat up inside the cowl? I am betting not much more than a 20F rise. Would be interesting to see some actual test figures on this. If it really is only 20F, that calculates (see page 5-7 in the Rotax 912 Operator's Manual) to be a little less than a 4% reduction of engine power. That is measurable but maybe not worth adding a lot of outside air ductwork, airbox, and carb heat controls. Just thinking out loud on an interesting subject.