Mine seems to have a lot of love for 30% cool power which I think has 23% oil content as well. I've read and been told that idling improves as the nitro content increases, to say nothing of the ability to swing larger props [8D]. Expense is an issue but the engine really hums on it and the extra oil affords some peace of mind at sustained high rpms. The instructions seemed to recommend at least 20% nitro, as I recall.