Quote:
Originally Posted by dan512
Take it easy on me madmaxx, I'm still learnig.
So if I get this right, the higher visosity is needed because that engine revs higher?
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Not exactly. In theory, the crank shaft spins on a film of
oil and doesn't touch the bearings. Not exactly true, I know, but that's the general idea.
When the engine is built, the bearing clearances are set either "loose" or "tight". A lot of race engines are built loose, supposedly making a little extra power while sacrificing bearing wear.
If the bearings are you loose, you generally use a higher viscosity, to make that film of
oil thicker to hold the crank in suspension.
Another theory I read is that a 40
oil will stabilize a hydraulic roller valve train a little better at high rpm's than a 30 will. Interesting theory, but I haven't seen any real proof of that.
Generally speaking, you need a thick enough oil to maintain proper oil pressure in all situations. If the oil is too thick, pressures will be too high, and the bypass port will be open all the time. But the pump and drive mechanism will be placed under additional strain the just isn't needed. That's when you hear about shearing the pin on the distributor shaft.