The pistons we used are 0.030 over (3.937 bore), so technically this is a 397 instead of a 392. They have an 8cc dome volume and a 1.080 compression height. The trick here is lowering the top ring land down by 0.280 inch and the forging strength to handle boost. The black skirt coating is called Armor Glide. It can reduce friction and make the piston quieter and more durable.