Originally Posted by Jetronic
Originally Posted by RDY4WAR
Group I and II conventional base oils have a higher pressure-viscosity coefficient making them better at withstanding high shock loads. The greater shear stress in the oil film of conventional base oils also promotes greater additive response (which is why conventional is recommended for engine break-in).
How much higher is the pressure-viscosity coefficient generally? and how uch worse is the viscosity index? There's a good chance the conventional oil is thinner before the pressure is applied and still thinner after, despite a similar kv40.
Given the same KV100. Generally in the applications that want a higher P-V coefficient, thinning of the oil and high heat aren't an issue. This includes dragstrip only nitrous engines and rear gears seeing an instant hit from a car launching off a transbrake. It also works well for making engine assembly gels. Once temps start to exceed ~230*F, a group III or higher base oil is going to be more desirable, as you noted, since no amount of P-V coefficient will make up for a lack of thermal stability. Oils like Driven GP-1 and Valvoline VR1 are excellent at withstanding heavy loads in a nitrous-powered Outlaw drag car making 2000+ hp, but wouldn't last 2 laps around Daytona in a NASCAR cup engine, despite only having 1/3rd the power, just due to the extreme heat they deal with.
