The only test I have done is with the MVVS 58. I went from 6800 rpm on a slimline for a DA-50 to a header and can (a very good one from MTW, not a hand made cobby one) and lost about 200 rpm. That is not scientific, I only got one test, there may be more power there if I adjust the carb. Also the reeds in the engine were on the way out so that may account for power loss. MOre testing to follow when I get the reed block fixed.

TF