Alan Johnson Performance Engineering Ford 4.9 liter 6 cylinder race head. Designed for drag racing only, and NHRA accepted for Competition Eliminator. These heads eliminate costly and unreliable welded V-8 style cylinder heads commonly used in this type of racing. 100% CNC machined, this head provides the latest air flow technology combined with the superior reliability of billet 6061 construction. They come with 2.180" x 1.600" valves, and 37cc combustion chambers. Completely CNC machined combustion chambers and ports ensure substantially increased power and acceleration. They come fully machined and ready to assemble. These heads are supplied with a one piece billet 7075 rocker mounting bar.