Bill, Jim, RV, thanks to all of you.

It is not have to be an OS engine. My question said OS just because originally I posted it in the OS forum, and because I've been happy with my 6 OS's so far....

This would be my first 4-stroke, an my main concern is the compared power. For us "newcomers" is kind of confusing. I buyed the concept of "more torque at low rpm", but, frankly, I don't understand it (and I already read Bax's article on the fact).

Even to make my own numbers is difficult, since not all manufacturers detailed this information, and it is very subjetive anyway. So I figured I could get some help from the forum about this very difficult subject (and I did, thank you very much again).

Jim, you're right, Joe Bridi did not think of a 4-stroke, it would be difficult to get it in there. There is plenty of room in my sport model thou..
Bill, weight is first on the list, so I will consider Saito as well
RV, the YS63 was the first one I noticed, since I read in another forum that it has quite the same power of my 46AX, so from my little knowledge, it looks that I wouldn't be wrong this way...

Keep posting your thoughts, it is great to have you there.

Thanks and regards,