Minn thanks for the opinion I will go with OS for my next 4 stroke, but as for saito neither my 100 nor my .91 have ever had any problems tuning them and getting them ready for the p-51 maiden, but only time will tell, I know the person who builds my planes is going to do a Top flite p40 kit for me after the escapade, Minn what would you suggest in what OS Engine size four stroke? A OS 91FSII pumped or maybe a .110? Its a larger aircraft and the builder has one but he put in a I Believe a large OS 2 stroke. And I was mistaken on prices, I must have been thinking of the FX series. Either way, like said above, all engines are pretty well suited and as mike said you really pick for your application which is a good point. Im not no vet in any way by far actually but still learning and will eventually try each engine brand.