barq
If you don't use any nitro then keep the oil content at 20% because the much lower fuel consumption means less oil flow through the engine. I have one engine (an ST 51) that's so economical it needs 25% oil to stop it from over heating.

XJet, thanks for the offer. I know some synthetics can be very good and the only one I've trusted in any of my engines so far has been a turbine oil but they're $28/litre for Mobil Jet Oil II and $20/litre for Shell turbine oil while my castor (Castrol M) is $8/litre.