ORIGINAL: TonyF
An available engine is the Evolution .61NX. It is very light for the power it makes. Don't run anything more then 15% nitro unless you add a head shim or two. Even 15% could use an extra head shim. Mine on the recommended header, pipe and an 11x7 APC turns 13,800 to 14,000. I don't believe anything that is as light will turn as high.
As to old engines not available anymore, my favorite was the O.S. .61F-SR ABC with the exhaust port raised. Great power for the time. But I have to agree, the Tigre G.60 ABC was a great motor. Glad a have a new one!
+1 on the above engine. I have seen it in action, and it delivers. From the same factory comes the Magnum .61 XLS. A bit heavier than the Evo, it turns 14,200 on an 11/7 APC/Mac's 10cc Quite pipe/15% nitro set up, and after 10+ documented hours, still cranks out the HP like it did on day one. Like the FSR, I am convinced that with some port manipulation, there is more power to be found from this platform. The Chinese engines are true ABC engines. (No EPA in China).
The real news for NEW available engines is the O.S. .65 AX and the Nova Rossi engines. Major power that does not quit!
-Robert