I wont ever touch RP after reading the articles I did...that and mobile 1 aren't what everyone thinks they are...the thinner the oil is (no speaking in weight but along the lines of the property of the oil and minerals added) the less protection it gives but yet allows the engine to spin more freely making more power...it doesn't make that power for a long time though because the oil breaks down sooner. I'd rather not make that extra 3 whp and keep my bearings living for the next many years...just my choice.