I know that most of the suggestions are for OS engines, but let me suggest looking at the Evolution .45. Dual needle valves, chrome liner, and good power for the low price. You can remove the weighted flywheel and use a 11x7 type of prop with good high end RPMs. I also flew mine with 10" props.

Just because it's scale doesn't mean you have to underpower it. I agree that there are times when extra power will save your butt....