Ok, the guy from autozone and my manuel said to use 10w30. But for high performance motors what should i use? I am looking at 350hp 302. Should i use a 10w30, or something like 10w40, 15w40? and what exactly do the number mean for oil?
If stock bearing clearances or just a little looser I would use 10/30 or 5/30 synthetic especially if there is a HV oil pump. Lass parasitic frictional losses from lighter weigh oils and better fuel milage to boot.
The numbers on the oil,lets say 10w30 means the oil has the ability to flow like a straight 10 weight oil in the winter but will also act like a 30 weight oil in the summer.A 5w30 oil is a little lighter and is better for cold weather starts while still providing 30 weight protection when hot.
If bearing clearance is not excessive the lighter the oil the better.The oil needs to start flowing as soon as possible.The most damage is done during start up.Your oil pressure at idle with the engine at operating temperature will allow you to make the decision if the light oil will be suitable for your engine.As for the ring situation,it is a catch 22,if ring tension is weak,more than likely light oil may seep past the rings,on the other hand heavier oil will cause the oil ring to work harder,acceleratoring wear of the oil ring.