I run R/C dragsters and use castor only in my engines. We do some crazy things to our engines. Like using 55 and 60% nitro and very little oil 3% or less. Synthetic just doesn't hold up to this madness The runs only last a couple of seconds for a very slow one 1.6 seconds for a competitive run 1:10 track which is 132 ft long. I've used Klotz and Castrol castor in my motorcycles and Castrol in my cars for ever with no problems in any of them. I think the problem when you get a lot of carbon from castor is overheating the engine. That formula in a previous post tells you why. If you get the heat and pressure up enough to break those bonds all you have left is carbon. That is the only time I see any deposits in mine. I tear down my engine completly after every race clean it out with B12 Chemtool and let it dry before reassembing it using a little castor. I started doing this because I noticed if I didn't the crank wouldn't turn as freely. I attribute this to the castor left in the engine starting to gum up. One guy at our track runs no oil in his top fuel engine during the actual competition. He runs 3% for the practice and switches to none during the rounds. Certain brands of nitro have a little lubricant in them for blowers. If you use that you don't need oil in our sport. That engine ran for over a year won the biggest event last year and finally gave up a bearing a couple of weeks ago after a run-away. Castor only in that engine. I don't think the synthetics would hold up. Castor might be sticky gummy goo compared to synthetic but it protects and sticks to parts better than synthetic in my opinion.

Griz