Actually if you can afford it I would suggest an .85 - .95 size 4-stroke... improved power, fuel consumption, and sound... will let you swing a bigger prop as well. If you can't afford that, pretty much any .60 - .65 size 2-stroke would work fine. Ask the guys/gals in your local club (if there is one), most of them, if they have been in the hobby for a while, will have one or two laying around they would be willing to sell.