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Message: [QUOTE="jimdawg185, post: 1169422, member: 757"] For your high HP engines... The most important factor in lubricant selection is Viscosity. The engineers from Navistar and Ford choose this spec based on mostly two factors. Load and speed.... Load is based on pressure over surface area. Speed is the actual velocity of the parts in opposing motion from one another (the bearing surface and the journal surface), not just the RPM of the engine. One of my friends at Mobil was telling me a story about their visit to John Force Racing. They were using a straight 70 in their race engines. The problem with diesel engines is those large journals make velocity much higher than it would be in a smaller journal engine. The bearing surfaces are traveling farther at the same rpm. In general higher speed would translate to lower vis, and higher load would translate to higher vis. So in general, until you make some serious power, 15 40 should be pretty solid. I would probably look at a 20 50 over 800, more so if the power comes on at a lower rpm. [/QUOTE]

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