I use 1/2 & 1/2 castor & Syn. with good results as with most engines I vary the % of oil & nitro depending on wheather it is a BB or plain bearing engine and what kind of engine make it is. But I run the older engines in my planes like ST.40-.60, OS .15-.35S, Mc Coy .35-.40, Johnson, Fox, K&B, and many more
I started to use 1/2 & 1/2 oil mixes in my combat engines with good results and less destruction on hot days in matches. Hope that answers your question. Take care, Frank