Hey guys, email Otto at [email protected]. He is the RCV rep in the US and is very knoledgeable on the care and feeding of these engines. I have a .90 that I have bench run and it is very smooth. I have a 16x14 APC on it and it turns a little fast. Otto says to run them under 5000 rpm. Also you want to run them on the rich side or they detonate. A 1.20 on a .60 size Mustang sounds like it might be to big foer the airplane. I talked to the factory and they recomended the .90 for my TF Sea Fury. A friend has a 1.20 that we have also bench run and it idles in the 800 rpm range after about an hour of break in. Don