I read this and wasn't going to reply, but since the score is 2-0 in favor of Saito I thought I'd better help even the score.

All I've personally run is YS, and they are the only 4 stroke I ever plan on buying. I am in charge of a fleet of 8 planes at my research job here at college and they all have Saitos, so I do have plenty of experience with them even though I've never owned one myself. YS's fuel system, though more complicated, really gives it the edge on power. It's a big edge too! Saito guys may come and say their Saito turns almost the same RPM with the same prop but they are probably using 30% nitro to get the same numbers as YS on 20%. True YS needs 20% to really run nicely, but it IS worth it. My 91FZ turns an APC 15x6 at 9,900 RPM very reliably; over 10k on a nice cool day. Can any Saito guys say their 91 will do that with the same fuel? Doubtful. I'd run up to a 61 2-stroke before buying my YS 91FZ and was frankly a bit scared of the power it had when I first ran it up. I was in awe... and I loved it.

If you can tune an MVVS engine to sing well you can tune a YS without problem. Spend the little extra cash and get the YS. You'll kick yourself later if you don't.

Carl