Excellent street, strip, oval track and truck or marine performance upgrade. Maximum torque and throttle response from 3,000 to 7,000+ RPM. Best for 347-427 cubic inch engines. Works with most standard components. Dart PRO1 20 Deg 210cc CNC heads for Ford small blocks are professional quality competition cylinder heads. We applied the airflow technology developed in our championship winning Pro Stock engine program to produce these state of the art heads. Exhaust runners are raised .135 in. for improved flow. Manganese Bronze valve guides are used for long life, and hardened valve seats provide durability with unleaded fuels. Features 2.500 in. and 3.000 in. exhaust bolt pattern. Assemblies include Stainless Steel valves, premium springs, locks, retainers, studs, guide plates and seals.