Both totally true. My point was only that big power and thick oil don't necessarily go hand in hand. How and where the engine is being used comes into play just as much as what it's capable of or how it's built. As for cylinder count it shouldn't matter to any great degree. Oil protects moving parts, and whether it's two cylinders spinning at 7000rpm or sixteen, the cam and crank and valves and rods are all doing about the same thing. The heat byproduct from combustion is also related to output, not moving parts count. Xhp puts out about the same heat regardless of what made it. (Although, you *might* be able to show that a small motor will have superior volumetric efficiency and produce less waste than a big motor. Maybe. )

quote Originally posted by thesameguy: The ideal is the lightest oil that doesn't fall apart. Anything more is just losses. Again, this is where engine oil analysis is useful. Put some oil in, beat the crap out of your car, send oil in for analysis, and let a microscope tell you whether the oil broke down or didn't.

I agree.

quote Originally posted by thesameguy: The heat byproduct from combustion is also related to output, not moving parts count. Xhp puts out about the same heat regardless of what made it. (Although, you *might* be able to show that a small motor will have superior volumetric efficiency and produce less waste than a big motor. Maybe. )

A smaller engine with fewer cylinders making the same power though, is probably doing so under boost and/or with higher compression. Greater cylinder pressure will amount to more heat/stress in the engine, and so such factors also matter.

Obviously, one should consider all the factors in play, and pick the best oil for the engine, based on them. Maybe that is a 15w50 oil, but it's unlikely unless it's a fully race prepped engine and you're going to be changing the oil very often. More than likely it will be a 5w30 oil, if it's an engine built with street driveability in mind.