KevinC cleared up my old info on parafin-base crude oil stocks in the above referred to post. Always remember, check anything I post with a REAL expert before you try it. That said, I've used nothing lighter than 10w40 for almost 40 years. I used straight 50w Castrol in the Fiat 1600cc hot rod motor, and it needed it at 8krpms. The undersquare (stroke longer than bore is wide) 2.6 puts a lot of pressure on the crank rod and main bearings, especially if boosted. I like a tough oil film and high oil pressures, and I'll live and die on castrol 20w50 until somebody proves to me that something else is better. I also really like the stock mitsu oil filter a whole lot better than any aftermarket filter, most of which I consider to be junk.

I will also note that a lot of the engines I have torn down that used Pennzoil/Quaker State were VERY quiet even though they had badly worn clearances, and even lifter that wiggled in the bore. All kept nice and quiet by the half inch of baked on sludge on the inside of the engine. I've pulled off valve covers that only had enough open room in them for the rockers to move, the rest solid with parafin goo, and the pan was almost as bad....