with our team race diesels we normally use 10% caster in our fuel .we have to clean the piston and liner about every 300 laps
this year at the team trials i used 8% caster ,2% caster 927, and 2 % automotive caster Edge seaSAE 5w-30US , it stayed so clean that it was hard to start with out a big prop each time it cooled off . the piston was spotless. went back to all caster , the piston got dark and cold starting became easier .had to go back to cleaning the piston every 300 laps