Maximum performance/full competition, unlimited oval and super classes. 7,000+ RPM, 400+ cubic inch engines. Dart PRO1 23 Deg 227cc CNC heads 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. Every intake port, every exhaust runner, every valve bowl and every combustion chamber is 100% CNC machined on special dedicated PRO1 castings. These heads are ideal for high compression, big cubic inch small blocks and are great for supercharged applications. Standard valve angle and spacing are retained to allow use of off the shelf pistons and valve train components. Hardened exhaust seats are compatible with unleaded gasoline. Manganese Bronze valve guides extend cylinder head life.