I have an O.S. .40 FP engine on my profile and I wanted to know if it would be capable of turning an 11X4 prop or if it would be better to just use a 10X4. If i try out the larger prop, what does one have to check to verify that the engine is operating as it should and isn't being overloaded or something?

Thanks.

varies from location to location and engine to engine...
how it is tuned, piped, etc. etc.

I use my tachometer more than I thought I ever would

and the type of plane as well.

for example, I like using a 46fx:

1)on my ddust (a spad delta wing built for speed), I use a 9x9

2)on my sport flier, i use a 11x6 or 10x8 (basically the same)

3)on my fun fly, i use a 11x4.

Same engine, different planes, different props.

Your engine should easily turn a 10x6 prop. I might also suggest a 11x5 or 1x4. If memory serves me, the .40FP is a bushed engine (not BB) so it might not be a stump puller... But the props that I mentioned above should be OK for it if the engine is in good condition.

Bob

three prop depending on what you want to do.
Speed, it's not ment as a speed engine but 9x8 or 9x7
sport. 10x6,-- do this one
power better know as pattern flying 11x5 or 11x4