Motorcycle oil is designed for high revving engines.
Mainly the friction modifiers they add to the oil, they use more robust chemically synthesized multi-weight chain modifiers for air cooled engines and pumps due to high temperature breakdown of the oil in air cooled engine and pump applications. The priciest oil is anti-foaming vane compressor oil for a supercharger or screw vacuum pump @ $20+++ a quart.
Car engine oil has anti friction compounds that prevents metal to metal contact better.
Motorcycle oil has friction compounds because motorcycles has wet clutches, and if you use regular car motor oil. You might adversely affect it's clutch or possibly damage it.
Car Oil Vs. Motorcycle Oil
Motorcycle oil is expensive, but it is formulated to last longer in two-wheel applications. Oil must perform markedly different functions in a motorcycle than it does in a car engine, which is why the oils are formulated in different ways.
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Function:
Unlike cars, most motorcycles use the same oil supply for the transmission as they do the engine.
Considerations:
The constant meshing of gears in a motorcycle's transmission tends to break oil down faster than normal operation in a car engine, which is why motorcycles require a specially formulated oil.
Effects:
When exposed to extreme heat and pressure, the oil's molecular structure begins to break down into its component parts, thinning the oil and reducing its ability to lubricate. This is true of both auto and motorcycle oils.
Additives:
Oil companies introduce a number of additives to motorcycle oils that car oils do not have, including PTFE, also known as Teflon, which coats the gears to reduce friction. This reduced friction and subsequent heat reduction helps to reduce oil breakdown.
Oil Friction:
Aside from their increased friction reduction, motorcycle oils have a clear advantage when used in bikes with wet (oil submerged) clutches. The friction modifiers in motorcycle oil help to prevent clutch slippage, which automotive oils actually encourage.
