ORIGINAL: aspeed
The older Rossi .15 motors had a rear rotor version and a front induction version and the FI always went faster in the glow form. Mostly I believe because of the extra drag of the rotor. It may possibly be the air being rammed through from the front and flowing/cooling better but I don't think so. The preferred motor was the RR because of an easier run on suction, but it was just slower. Now at least one F2A motor has done away with the inside race of the rear bearing and it rolls directly on the crankshaft. This saves some moving weight. The diesel team race motors still like the RR because of the crankcase stuffing improvement giving better mileage, but they never revved quite as high as the glows, running higher pitch props. I never had a Killer Bee, is the reed valve system different than say a Baby Bee/Surestart? Usually reed valves flutter after about 18,000 rpm and can't keep up. I like Japanmans setup, good results?
A lot of things have changed since the baby-bee with regard to intake. The holes are bigger, material for the reed is different, the shape of the reed is different etc. I don't think it's an issue anymore, people are running some reedies over 22K now.