Change Really is GoodFor those of us who once cherished a set of Power Pak heads, only to forsake them when the double-hump fuelies versions came along, Vortec heads are another step in the evolution of the small-block Chevy. And while these heads were designed to increase the power and fuel efficiency of pickup trucks, they outperform any previous production head, and many of the performance designs available. That's technology worth learning about.
We'd like to thank Ken Casey of Burt Chevrolet for his help in preparing this article
GM Performance Part Numbers for Chevrolet Vortec Bow Tie Heads* If you're looking to update an early small-block Chevrolet with Vortec heads, here are some part numbers that will help:
* 12464298 Aluminum head, with 62cc combustion chamber, raised runner port volumes of 210cc intake and 78cc exhaust, 2.00-inch hollow stem intake valve, 1.55-inch sodium-filled exhaust valve, lightweight retainers, angle plug location, 3/8-inch screw-in rocker studs, either center-bolt or flange-bolt valve covers may be used. No heat riser passage. Casting number 12367713.
* 12497186 Bare head, same as above, but no springs or valves.
* 25534421 Cast-iron head assembly. Intake ports are 185cc, exhausts are 66cc, and combustion chambers are 65cc. Casting number is 25534351C.
* 25534351 Bare head, same as above, but no springs or valves. Casting number is the same as previous head.
* 25534431 Cast-iron head intake ports are 215cc, exhausts are 84cc, and combustion chambers are 65cc. Casting number is 25534371C.
* 25534371 Bare head, same as above, but no springs or valves. Casting number is the same as above.
* All GM Performance Vortec heads have 2.00-inch intake and 1.55 exhaust valves with five-angle valve jobs. Intakes have 45-degree, .060-inch-wide seats; exhausts are 46-degree, .080-inch-wide, and are induction hardened. These heads have provisions for center and perimeter bolt valve covers and dual intake manifold bolt patterns.