RE: Rossi .81 FIRE
the rossi .81 engines aren't stroked they are just bored.. most were set to run at 21-22k rpm, yes the piston is heavier...lets get real, this for fun speed airplanes not endurance racing right? i believe someone has taken ducted fan middle case with sleeve/piston and rod and assembled it with standard front intake crank etc, this takes all of five minutes to swap out...you can use some cutdown wood props to run and set approximate pipe length, then buy some carbon props based on your test runs, and intended airframe, check headshims on engine and add two thick ones.. it will take the 25 percent nitro with them installed.. contrary to a lot of tales told.. rossi ducted fans have been run successfully with high nitro in boats as well