I have a K&B Sportster .65 drone engine on one of my airboats. I like how the engine sounds and it certainly moves the boat well. I've got the itch to collect another engine to try on the boat for a bit more speed. I havent gotten all I can from the K&B, but I'd like to have a plan B in case I cant get more from it. The K&B turns a MA 12x8 at 9400 on 10% nitro. It does a little better with APC props - it turns a 13x6 APC at 10,400 on 10% and a 13x5 around 10,600 or so. I dont want to run a prop larger than 13", but am not opposed to a 12" prop swung faster. What engines would give me say 1,500-2000rpm more than my K&B on the same kind of props? Is 12,500rpm too much to ask from a .60 sized engine on a 13x6 or similar size prop?

I have tested 11x7MA, 12x6MA, 12x8MA, 13x5APC, 13x6APC, and have a 13x7APC to try yet. Speeds were 20mph, 22.1mph, 24.9mph, 28.5mph, and 31.9mph respectively. 13x7 is untested so no numbers for that yet. (I dont use the MA props anymore - they were cheap and good to use for basline testing and learning how to drive it)

I'd like to have the power to get it to 40mph, but given the prop loads of a 13x6 to a 13x7, I think the 13x7 will be a loss of speed and thus my hunt for another engine..

Thanks for any that have any input.