The Phase 2 Bow Tie cylinder head (casting P/N 12480034) has the highest performance potential of any cast iron Chevrolet head. It is intended for off-highway applications only. Although the Phase 2 cast iron Bow Tie cylinder head has the same casting number (12480034) as the Phase 1 head it replaced, there are several significant differences between these two heavy-duty cylinder heads. The Phase 2 cast iron Bow Tie head can be identified by its redesigned outer water jacket wall with a machined bar between the exhaust manifold flanges. (Phase 1 castings have a raised parting line between the exhaust manifold flanges.) The area around the tapped water temperature sensor hole is also machined flat on the Phase 2 head.
The Phase 2 Bow Tie head has a revised combustion chamber design with a true volume of 64cc’s. The quench areas beneath the spark plugs are filled to increase compression in competition engines. The intake valve seats are machined for 2.02" diameter valves; the induction hardened exhaust valve seats are finished for 1.60" diameter valves.
The intake and exhaust ports are identical in Phase 1 and Phase 2 cast iron Bow Tie heads. The 184cc intake runners will satisfy the airflow requirements of most competition engines while enhancing throttle response and mid-range torque. In unmodified form, the Phase 2 Bow Tie head will flow more air than any production cast iron small-block head. Extra-thick wall sections allow the ports to be enlarged to increase their flow capacity. The manifold heat riser passages are deleted in Phase 2 Bow Tie heads to produce a cool, dense intake charge.