ORIGINAL: les40
I stand corrected. The weight I specified for the OS .91 is WITHOUT muffler. I cannot find the spec. for the muffler weight. but I would imagine that it would put the engine a few ounces heavier than the Saito 100. Not sure though. At any rate I would estimate that the power to weight ratio of each engine is about the same.
Another thing I would like to point out. My Saito 100 is rated at 1.8 hp. I can get about 1.7 hp out of it. My 2 stroke .46 is rated at 1.7 hp but I can only get about 1 hp out of it running a prop that will give enough thrust such as an 11X6. I could put a 10X5 on it and get more rpm and more calculated hp output but the smaller diameter would produce less thrust and wouldn't be practical. So the lesson learned is that you can get about 94% of the rated hp out of a 4 stroke but only about 60% of a 2 stroke's rated hp.
by towerhobby the os 91fx is 24.3 with muffler
by Horizon saito 100 20.9 with muffler.
Another thing to keep in mind HP is worthless without max torque being in the same rpm range for all but flat out speed.
I'm pretty sure with the above 2 engines turning 14x8 props on two identical planes of the same weight vertical at full throttle that the 4 stroke will be pulling after the 2 stroke stalls maybe not but I think it will
but I'm also sure that the 2 stroke will out run the 4 stroke in a flat out speed race with the same two planes the 4 stroke will get the lead from off idle but will give it back once the planes are at max rpm
there are just too many variables to make a comparision between the two