Thanks for the great first-hand info BK. What I think your post reinforces is that velocity stacks may have a beneficial, or non-beneficial affect, and I know for myself, I wouldn't even bother to try one unless I was going to do a precise test using either a dyno, and with lack of that(the most likely case), different props to test at different RPM ranges....but I think you'd find on our engines that the benefit (if you got it tuned right) would be so slight, it might not even be accurately measurable on a tach.
Do you know the best case % gains you were getting with the MX engines?
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Bill Pryor
Bill, the average HP gain with the properly tuned intake velocity stack would probably be around 3% (or 1.5 hp on a 50 hp engine). But there are other things to consider, like throttle response, width of power band (or useable power range), fuel consumption, etc.
Basically the higher the desired peak TQ rpm the shorter the stack had to be. But like I said, you could have a great performing stack that made big gains at a steady rpm that would absolutly ruin the throttle response. It is definitly a delicate balancing act.
BK