hi the super tiger 51 has amazing power-   as big an engine as you would put into a 40 size plane-  i broke my 51 on an 11-5 apc by total mistake-it took me 5-6 tanks of  15% to get it to idle and run-but wow does it run-it comes close to power in some of my 61 engines  -i always remove the baffel and match the exhaust port to the muffler -by grinding the muffler out-and making the exhaust exit a bit larger-on all glo engines i own- she turns 13,200-13,400 rpms-TRY IT YOU WILL LIKE IT-that is on a stock muffler