the 63's are best run up near the 10,000-11,00 range. This is the RPM the timing and the cam is set for. Yes it will get loaded harder and run, but it will increase the chance of something failing and when there is a failure or you run it lean...like running it out of fuel...The failure will be much more severe.

Its common on 4 stroke engines to be setup this way. The larger the displacement the lower the rpm. The smaller the displacement the higher the rpm.

Matt is a good motor guy, but I suspect the engine is working pretty hard at that rpm for a 63. If it was a 110-170 it would be better at that low rpm. Another issue is heat, I suspect knowing Matt he is flying the model at reduced power settings, and is not flipping and flopping around doing much if any 3D stuff. Since he has experience with engines and knows what is going on the chances or a problem are less, however the 63 is designed by the factor to run at about 10-11k and the noise produced by the 12 and 13" props at the 11k range is much lower than the 140-160-170 engine turning the 16-17-18 in props at 8500rpm

On 4 stroke engines the cam gear helps determine the timing. Its not like a 2 stroke. Example. an 11-7 will turn about 11k on the 63. a 12-7 will also turn about 11k on the 63. The 12" prop definitely has more pull than the 11" yet the engine ends up being limited by its timing. You want to run the engine in its happy place. For these small 4 strokes the higher rpms are the happy place. I just have way to much experience with them. Can you make them do other things yes...but you are taking the engine out of its envelope and when it comes to higher loads this means shorter life on the engine. As for the 91's and 110's pushing 11k is not good on them either they are happy back in the 9500 range. maybe just under 10k. The newer 110S seems to do well at 9200. The 120's around 8800, the 140's about 8400-8500. The 160-170's around 8100-8300 is the sweet spot. 4 strokes are for grunt. But they are designed around a certain range of performance.

Matt is a good friend of mine and I'm not condemning his use of the engine. But when and if it breaks Matt also doesn't go running to the manufacturer complaining about the failure. he knows what he is doing and its being run a bit too loaded for my taste. Again the timing is optimized for the rpm range intended. Just like your car. Picking a prop is like changing gears in the car. The engine wants to run at a given rpm for its power, and performance. Run it harder at a higher rpm and its not efficient, load it down lugging it going up a hill in 5th gear at 30mph well it doesn't like it as much. Yes it will do it....but not what the engineer designed it to do.

I have a 63 that has probably 500-600 flights on it over the course of several 4-5 years and it has never ever had anything done to it other than a new valve cover gasket and keep the tappet clearance set. I use the 12-8 or 12-9APC on 30% heli and have used this prop and fuel combo since it was new out of the box. Tried some others props and it was better for the model its in on the 12-8 and 12-9. RPMS are around 10,500

Troy Newman
Team YS