The way you tune your engine is far more important than whether you run castor or not -- but here's *my* take on oils.

For a ringed engine you *can* run fully synthetic. As a result, you'll get a little more power, a cleaner engine (and exhaust), plus end up with less oil on your plane.

So long as you are careful with your needle, a ringed engine run on a *good* quality straight synth (which rules out *some* fuels) will last pretty much as long as an engine run on castor or castor/synth blend.

However, there's no way to guarantee that your needle will always be set "just right" and the occasional lean-run is a fact of life with model engines. Sometimes it's caused by a change in the weather, a split fuel line, a clogged pressure nipple, or maybe just some dirt in the fuel system somewhere. One thing's for sure, such things do happen despite our best attempts to keep everything 100%.

When you get a lean run, just a couple of percent of castor *might* save your motor from some undue wear (or worse) and it will certainly provide superior after-run protection for your bearings.

But what will this tiny amount of castor do to your engine under normal conditions?

Nothing at all.

It won't gum up your ring, it won't cause any perceptable reduction in power and it won't produce much more than a few extra drops of residue on your plane.

So, unless you're a master engine tuner and are dedicated to significant amounts of preventative maintenance on your fuel system -- why not enjoy a little insurance in the form of a *good* quality synthetic plus a trace of castor?

Which begs the question: what oils are *good* and how much is "a trace"?

Well fuels made with Morgans' pink oil (Omega) will have way too much castor for your engine. I believe they run a 70/30 ratio of synth to castor -- that's a lot of castor. When blended at the recommended 17%-18% by volume, over 5% of your total fuel volume will be castor oil and that's almost enough to start gumming your ring.

Klotz SuperTechniplate has an 80/20 blend of synth/castor which puts the total amount in your fuel down at around 3.4%, but personally I'm not a Klotz fan for a number of reasons.

Right now I'm using CooperFuels "Plus C" lube in all my fuel and have been over the moon with the results, so that's what I'll be sticking to -- although I'm sure there are other high quality castor/synth oils that will do the job for most folks.