Manley pistons are machined of high strength 2618 material. Each design is lightweight yet robust enough to deliver long service life. Perfect ring groove to skirt squareness is achieved through our unique "one fixturing" manufacturing method that assures maximum horsepower. Roundwire locks, tool steel wrist pins and pressure balance grooves are included with every set at no additional charge. Note: Compression ratios for 4.6L are calculated at .008" deck clearance, a 8.933" deck height, and a .036" thick compressed head gasket.