Can anyone tell me what the acceptable SKIRT to Cylinderwall clearance is for a cast aluminum and Hypertechnic piston. This would be going in a SBC 400 with pretty much stock heads, cam, etc. Is there a definite minimum and maximum?
I have run cast pistons at .007 piston to wall. But like Greg stated it would have piston slap on cold morning start ups. That engine started using a qt of oil between changes at about 10,000 miles. So if you are running big clearances like that you really loose longevity. So if you building a grenade engine they will work.
I have a engine right now with hypereutectic pistons in it with .0055 piston to wall. I have not started in on a cold morning yet so i am not sure about cold piston noise but it's in a car that will only be driven in the nice weather. It was quiet on the test stand though.
If you are setting up a new engine, go by the specs. If it is a junker race engine or something to get by, specs can be cheated a little. I have a friend who built a junker race engine from a worn 400 block with STOCK cast pistons with .008 slap. Put a big ole solid cam in it with some home ported to the max 041 heads on it and went racing. Ran 12.40 in a 3400lb Malibu with 6500 RPM shift points. Would it run long like that? Probably not, but it was put together with junk parts and buying nothing new. He had lots of fun with it for no investment.
I would go for 0.0015" side clearance with cast pistons. That means a 0.003" feeler gage will fit tightly between the pistons and a cylinder wall without rings installed. But you should check the piston spec sheet.