Speed Pro Hyper coated skirt pistons compatible replacements for Chevrolet 454 - 4.250" bore @ (STD) Domed head .230" high w/2-valve reliefs. 1970-76 Car (USA) 1970 454-LS6; closed chamber heads Higher compression, longer life. If you're looking for pistons with an unbeatable combination of performance and value, then Speed-Pro hypereutectic pistons are for you. These pistons are manufactured from FM244 aluminum alloy, which contains 16 percent silicon for greater strength and wear resistance. They're also molded in the latest permanent-mold technology to ensure the precise fit and tight bore clearances that today's top engine builders demand. They're ideal for use in high performance street, bracket racing, and oval track racing and will work perfectly with normal ring end gaps.