We've used it on 600+ HP round track engines, with good results. It's designed to be used on the inside of oil-filled electrical transformers, so oil resistance is not a problem. It is necessary, however, to smooth out the casting roughness before it will stick properly. Be ready to spend a LOT of time with a die grinder on the inside of the valve valley, and inside the crankcase. The primary advantage comes from the smoothing, not the paint, IMHO, as it dislodges any residue of casting sand stuck into the rough surface of the metal. At least some of that sand gets washed off, and circulates itself through the lubrication system. on a 50+ year old engine, I doubt if there would be much left, but on a brand-new casting it probably has some benefit.
Jerry
