ORIGINAL: bruce88123
I don't remember what engine you have but a 10x6 is pretty typical for a .40 size engine. A 10x9 would be way off for a .40 IMO.
Tell us your engine mfg/size again and the type of plane for us forgetful people.
I have a sig lt-40 with a thunder tiger gp .42 bolted on front there. I gues a 10x6 is going on the shoping list