ChrisSpad

I've seen several people say they run 18x8's on the 26cc ryobi 4 strokes, and they turn about 6000 rpm, thats the same that mine does. (older version, metal oil sump)
At any rate, someone suggest that since its a 4 stroke, it should have alot more torque, and swing a bigger prop, which sounds reasonable to me. So, i had a 20x12 zinger laying around, and put it on the 4 stroker. It spun it fine, at 5200 rpm, which isn't gonna set the world on fire, but its considerably more thrust than an 18x8 puts out, and brought the bhp up from about 1.3 to almost 2.0.
Has anyone else tried this, and whats the experts' opinions on whether it'll hurt the engine or not.
Ryobi doesn't offer a torque rating on their engines, but honda does. Their gx 31 puts out max torque at 4500 rpm, and the gx 25 at 5000. Does it make sense to you guys to run the engines at or close to the max torque rpm?

Thanks

SuperJ

Local guy flying a new style Ryobi in a Sig clipped wing cub is doing the same thing I think he is flying a 22 X 10 turns about 5400rpm but he has cleaned up the head on the motor and is using a bigger carburetor than stock. He said if you want to wind it up with a small prop the only way it pulled hard for him was with the cam timing retarded. He is currently experimenting with mousse can tuned mufflers, intial results are positive plus 150 rpm to 5550rpm but he thinks fine tuning of header length and stinger diameter will improve on that even more. His cub flys almost as well as mine with a hopped 30cc Homelite two stroke and his sounds scale to boot. If I wasn't interested in improving power for flying on floats I would give a Ryobi fourstroke a shot myself. He is watching his cylinder head temp and oil temperatures carefully for any sign the engine is being lugged too much but given the fact that its February in Minnesota the engine is overcooling if anything. Time will tell if the exhaust valve life is shortened or if overheating becomes an issue when its 90 degrees out this summer.

ChrisSpad

Thanks J,

I am gonna go ahead and cut the bellhousing off. I'll build something for it.
Man, the sound is just awesome.