These cylinder heads are cast from the same virgin 355-T6 aircraft alloy that is used in Dart Pro-Stock heads. These Windsor style heads are available with CNC machined or as-cast ports. Standard valve angle and spacing is retained for bolt-on compatability. Exhaust runners are raised 0.135” for improved flow. As cast heads are bowl blended on 5-axis machining centers. Manganese bronze valve guides are used for long life, and hardened valve seats provide durability with unleaded fuels. PRO 1 Comp series aluminum cylinder heads feature high-flowing as-cast ports with profiled valve guide bosses and are bowl-blended on 5-axis CNC machining centers. PRO 1 CNC Pro series cylinder heads are based on dedicated castings which are fully CNC ported and have fully CNC'd chambers for maximum airflow and consistency.