Nun45,
you can use the OS.91 and it is a very good engine-but if you want max.power and performance-get a Rossi .90 or 1.05-heres what you can do-use 3 head shims-if you don't like the Rossi carb,(although it is a good carb)-a OS.91 carb can be used-Break the engine in just like the directions say-use 5% nitro fuel with 8 ozs. of extra castor oil added to it- a OS.91 will turn a Byron fan rotor at around 19,500-20,000 rpm. The Rossi .90 will spin it at 22,000-a lot more power.



Jackjet