Oops, almost forgot a very important point in this oil discussion! The Wiseco big bore kit uses their wonderful forged piston (YEA!!!), which has different expansion characteristics from the stock, cast piston.
All forging alloys, while stronger than any cast alloy, including hypereutectic castings, tend to have greater expansion when heated to operating temperature. This means that skirt clearance with a forged piston must be greater than with a cast piston. (If you were to put mufflers on a drag race engine, you'd scare yourself with the piston rattle before the engine gets up to temp.!)
Amyway, in a forged piston motor, I always run thicker oil over one with cast pistons - straight weight if I can find it.
Incidentally, TRW forged pistons are made with a different alloy from the "California" race pistons, such as Wiseco, JR's, Diamond, Ross, ect. This different alloy has more silicon in it, so it expands less than the other forged ones. The others are slightly stronger, though. TRW's are run with tighter skirt clearance than those other forged jobs. That's great for a hi-po street motor.
