RE: Cool Power 4 stroke fuel; nitro and oil content?
Yeah, synthetic works fine. Unless you have a lean run. But in RC you just shut down and land. In control line, you can easily ruin an engine with a few lean runs and no castor. With some of the older iron piston/liner engines, you really do need the castor (and lots of it) - in fact, if your engine is an older, well used iron piston engine, one tankful of synthetic oil will ruin it - by stripping away all that varnish that was providing the compression!