Cruel Power green fuel? This is only about 17% straight synthetic fuel, and it has no castor oil in it whatsoever. This is, by Morgan Fuel’s own ads, inappropriate for ABC, ABN (and AAC) engines, but this is exactly the fuel many use. Low lubrication fuels account for a lot of the cases of nickel liner separation in the OS FX, SF series for example. Not only that, but a number of pilots really run their engines lean in the air, and this compounds the problem, and leads to premature failure of an otherwise good, strong engine. A good high quality castor oil would only be found from Bakers AA castor oil and Klotz Benol racing castor (sold since 1958), the very best (pure). Generally speaking smaller engines (.19 - .65) use more oil content than larger engines. 20% oil is a better fuel offering a cooler running engine, more powerful leaner runs with a larger margin of protection. Castor works efficiently when the engine is at operating temp, not good on a cold engine. Bad some decades ago, the older engine fuels had more castor (20%-29%) and today many freeflight and control line engines running wide open use more oil content.