Whats better for a 91fx a caster mix or fully syn like coolpower? I really like some castor in my .61fx abc but with the 91 having a ringed piston would the castor be needed? I dont want a gumed up ring on the 91 and have heard that castor is not needed with ringed engines. Also any body like the Byrun fuels as that is what my local hobby shop carries other than the coolpower?

Ive evan thought about mixing the two, any comments on this?

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.

I would run at least 5% castor in my fuel for most engines. You can get AA castor or Klotz Benol or other racing castor and add it to your fuel. Some folks still don't get it, but when you get a lean run, and you probably will from time to time or in high temp, the castor will form high temp polymers and protect your engine quite well. A lot of fuels are a bit low on total oil, or the oil is not very good in the first place. Also, you can run 10% nitro, which is plenty for many applications, 15% better for my Saito FA091S engines, but in 4-strokes, if you use castor, use under 4% and just 2% is about best. I know a lot of folks run all synthetic, but if you run green snot at about 17% oil, you will enjoy your engine less time that you had hoped. You have a nice, powerful engine. If it were mine, there would be some good castor in there as well as synthetic oil. These comments refer to NON-ringed engines. Non-ringed engines still benefit from castor and with proper maintenance is no problem for these engines. Putting 17% oil green fuel in nice ABC, AAC and AAN type engines is not really a good idea in my experience, despite the "slightly rich" runs claimed by a number of modelers for this 17% fuel( probably true), but a lot of modelers do not run their engines rich with this type of fuel. In a hot flying day or lean run, there is a good price to pay with these engines. The old fuel mixing dinosaur.

This is my experience with castor in a ringed engine. I ran an Enya 45 with twin rings on a dose of 25% all castor for all it's life. It had quite heavy use because it was in a competition CL stunter so there was much flying done with it. Every year or so I'd strip it down, clean out the carbon build up and put it back together for another year or so. I never encountered sticky rings, and it was only after maybe a few hundred hours that it began to be harder to start (which in my case meant maybe 5 or so flicks instead of one). A new set of rings and it had a second life.

Lately I've been using an ST G51 with a single ring but still on 25% all castor. It's only done about 30 hours so far but no signs of a sticky ring. Word has it that even a relatively small amount (maybe 10%?) of synthetic in the total oil quantity will keep the engine clean inside (the carbon build up).

I uased to be a believer in high-oil percentages and generous amounts of castor but I'm changing my mind these days.

You sould try a *good* synth oil with just a trace of castor at much lower percentages (assuming a BB engine), you'll be surprised at how much better your engines will run, how much extra power they'll put out, and how they still last virtually forever.

Not only that, you'll save a snot-load of money on your fuel costs.

I used to mix 18%-20% oil (including castor) into my fuel and it cost a small fortune. CoolPower Pink (castor/synth blend) is around $65/us-gal here in Kiwiland. That 3.8 litres of oil only makes 19-20 litres of fuel and I can burn that in less than a month (I fly a lot :-).

Since switching to a "better" oil and using less of it, I'm able to mix over 30 litres of fuel from a single 3.8 litre jug of oil. What's more, because there's more methanol in each unit of fuel, I get the effect of running about 12% nitro, even though I only run 5%. Some of the guys run 0% nitro and their engines perform better than when they ran CoolPower oils (20%) with 5% nitro.

In a land like Oz and NZ where nitro is mondo-expensive, being able to mix *cheaper* fuel that produces more power with no discernable bad effects makes a hell of a lot of sense.

Yes, keep your 20-25% castor for those old lapped iron-piston and/or bushed engines, but today's modern ball-raced ABC/ABN and ringed engines just thrive on a lower percentage of better oil.

I've run the hound out of K&B 4011's (Dykes ring) with Sig Champion 10% nitro 20% 50-50 oil with no problem.

Thanks guys, I appricieat all the input.

I stopped using castor in the very early eighties because of the mess it made of my models and have never even considered going back. I have never in all that time had an engine wear out or falter in any way. For 99% of engines castor belongs in the stone-age.
For me the horrible job of removing the mess from my models after a flying session was enough to put me off for life. The one exception being the Moki 210 in my Extra 300s. Just M.O.H.O.

All my engines look like new, despite using a small percentage of castor in my fuel -- I just take care not to spill oil/fuel on them when I'm filling the tank or starting them. The oil then comes out the exhaust pipe and disappears onto the plane or into the air.

I hope everyone is still talking in reference to RINGED engines....