The XDP Heavy Duty High Boost Valve Spring Set XD388 is an essential upgrade to strengthen and gain control of the valvetrain on your 2003-2010 Ford 6.0L/6.4L Powerstroke. These valve springs deliver improved valve control over a factory valve spring with increased spring pressure to minimize valve float. Each spring endures a stress relief process and is computer load mapped to provide a high-quality product with long-term durability. Tested within 1 lb of seat pressure, the XD388 comes as a complete set and includes XDP's 1-year unlimited mileage warranty. Valve springs only, this set re-uses your factory retainers and locks.