RE: Piped Super Tigre .51
I have not tried it on the ST51 but on ST90, 3000, 3250 and G4500 and all other 40-50 sized engines that I have tried a pipe on gave me about 1500 rpm more compared to the stock quiet muffler.
Engines in that size that I have tried with a tune pipe are Irvine53, MVVS49, Webra61 and maybe some more that I dont remember. All these engines responded very well to a tuned pipe.