This production Vortec iron cylinder head was first used on the 1996 pickup truck RPO L31 with fuel injection. The intake and exhaust port are very similar to Corvette 350 LT1 heads. America’s favorite high performance cast iron small block cylinder head offers big power and bigger value. The Vortec cylinder head's fast burn combustion chamber and high velocity ports combine to produce big horsepower out of the box. The Vortec head can be mildly ported for additional performance and can be milled up to .040” for increased compression ratio. This head includes 1.94” intake valves and 1.50” exhaust valves, springs and retainers, and pressed-in 3/8” studs. This head with compatible valves flows more air than bow tie head P/N 10134392, but the casting may not be as durable. It is a 20 to 40 horsepower bolt on increase over earlier cast iron small block heads. The water passages are the same as the original 1955 small block design. The eight-holt intake bolt pattern is totally different than the early model V8 12-bolt design. The Vortec head REQUIRES a Vortec style intake manifold due to its improved manifold mounting flange and gasket design and raised intake ports. It is not recommended that the heads be modified to accept early design intake manifolds (They will never match up right.). Use new manifold P/N 12366573, 12496820, 12496821, 12496822, or any others that we have listed below for correct matching to the Vortec head. Vortec heads fit all small block engines produced 1955 to present, excluding LT1/LT4 reverse coolant flow engines and current LS1 style “GEN 3” engines.
Technical Note: The valves seats in these heads can be machined to 2.02” intake and 1.60” exhaust. The rocker arm studs can be pinned or drilled and tapped 3/8”. These heads require the use of self-aligning rocker arms. (Casting P/N 10239906 or 12558062) (65 ft./lbs. head bolt torque)
Please Note: The casting number myth debunked:
The myth is that there is a difference in the head performance produced by these two castings.
This myth was started by some Magazines that didn't do their homework before publishing their articles.
This is the truth the whole truth and nothing but the truth. So sayith the Grand Wizard GM and his Apprentice Wizard Chevrolet.
10239906 casting has one large single hump.
12558062 casting has 3 small humps.
If either of these two castings have not been altered by GM and the part number changed from 12558060 or altered by someone else (previous owner, etc.), the heads produced by either casting will be identical except for the external cosmetic difference. Both castings are used to make the 12558060 Vortec heads which are the true unaltered Vortec heads.
Heads from both castings come out of their cast IDENTICAL except for the minor cosmetic external differences!!!!!!!!
