I agree with Red, lubricity is a career unto itself therefore I follow the manufacturer recommendations (Roush) which is 10W30. Excellent thread. Another interesting side topic is Roush perfers the Motocraft FL-1HP over the the FL -1A. The reason being the FL-1A which is readily availabe at any store for a third of the cost has the internal releif set at 9-12 psig where the FL-1hp is set at 20psig. Roush feels that engine operating near max rpm generate higher
oil pressures and therefore they do not want the
oil bypassing the filter.