i would like to try a 4-stroke in me helicopter for an experimental change.what would be equal 4-stroke to a 0s .50 fsr and would i have to really change my clutch gear?i just want to be able to hover and i little attitude flying.

I think you would have to go to at least a .70 to get the same power. It would be more of a pain than it is worth. I don't think you would have the revs or the power you need.

The nexus came out with the 53 4 stroke and it did not have the power to make it worthwhile. To replace the power of the OS 50 you would need a YS 91 which would not fit. No 4 stroke will replace a 50 and fit.