Chevy Small-Block V8 |  Cylinder Heads |  12480034  

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12480034  - Phase 2 Cast Iron Bow Tie Head

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The Phase 2 Bow Tie cylinder head (casting P/N12480034) 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 64ccs. 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.  
Technical Notes: The valve spring pockets in cast iron Bow Tie heads are machined for up to 1.50" diameter competition valve springs. The rocker stud bosses are tapped for screw-in studs; studs and pushrod guideplates are not included. Use GM Performance Parts studs P/N3973416 (3/8") or P/N3921912 (7/16") and hardened pushrod guideplates P/N3973418. Use 5/8" hex-head spark plugs with tapered seats and 3/8" reach. A bare casting weighs approximately 42 pounds. Valve seats are heat-treated.  

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