I have been looking at what is considered a good oil and I found this "independent test report". http://540ratblog.wordpress.com
I am not sure I fully believe that this test is all you need to worry about for oil, i.e. Mobil 1 0W30 racing is ranked 93rd and in the modest section.
He did make what I think are some interesting observations..
"The old rule of thumb that we should have at least 10 psi for every 1,000 rpm is perfectly fine. Running thicker oil to achieve more pressure than that, will simply reduce oil flow for no good reason. It is best to run the thinnest oil we can, that will still maintain at least the rule of thumb oil pressure. And one of the benefits of running a high volume oil pump, is that it will allow us to enjoy all the benefits of running thinner oil, while still maintaining sufficient oil pressure. A high volume oil pump/thinner oil combo is preferred over running a standard volume oil pump/thicker oil combo. Because oil “flow” is our goal for ideal oiling, NOT simply high oil pressure."
"With the exception of high rpm hydraulic lifter engines, almost no engine should ever need to run oil thicker than a multi-viscosity 30 weight. The lower the first number cold viscosity rating, the better the cold flow. For example, 0W30 flows WAY better cold than 20W50. And 0W30 flows WAY better cold than straight 30wt, which is horrible for cold start-up flow and should be avoided at all cost. And the lower the second number hot viscosity rating, the better the hot flow. For example, 0W30 flows WAY better hot than 20W50."
I also spoke to Royal Purple & Joe Gibbs to get more information about oil for my engine. They basically said the same thing. Running less than 0.025 clearance for main and rod bearings use a 10W30 oil, >0.025" use 10W40. A stock / non-rebuilt engine might have to use a 15-20W50 oil. You might need to look at different qualities for flat cam followers. Then there is the debate on oil filters....
Original Post