Castor 927 is a blend of Castor and Synthetic Ester Oils. Benol is all Caster oil. The reason why that Benol says for Race Engines only is becuase it burns dirty. I think they just figure a Race Engine will be taken appart, clean, tolarances checked, and reassembled enough that the dirty buring is not a probem. I wouldnt worry about it just run it. I would let my tank get about empty before putting the fresh fuel with Benol in. Klotz's web page says that Benol doenst blend with petrolum based oils. It also says that Benol Starts to seperate from the fuel at around 35 deg F.