Where do you get your castor oil so cheap? I used FAI 80-20 for the speed class, and it required a different head than the very high nitro fuels that were used at the time. It was a trumpet shaped combustion chamber compared to the bowl. We had to use a #2 Rossi head. Nothing else would work, and the headspace had to be within a couple thousandths of an inch.. Otherwise it ran fine, an when using 10% nitro fuel as the rules are now, there was no change in speed. RC motors may suffer with a more unstable idle. We had to devarnish the motors every month or so. If I would use zero nitro now, I would use mostly synthetic with maybe 5% castor even with steel liners.