Vortec Cylinder Heads. An easy way to gain 20-40 horsepower on any 1955-and-newer Small-Block Chevrolet V-8 (except later-style LT1/LT4 engines with reverse-flow cooling) is by installing a set of Vortec cylinder heads. These value-priced cast-iron cylinder heads use modified combustion chambers and high velocity port technology to provide improved performance. Vortec cylinder heads significantly outflow non-Vortec service replacement cylinder heads and earlier OEM cast-iron heads. These cylinder heads are ideal for applications up to 350 horsepower, but they require Vortec-specific intake manifolds. Cast Iron Vortec Cylinder Head Assembly. Completely assembled with 1.940/1.500 valves . Uses bare head 12529093. 64cc combustion chamber. Straight spark plugs . No heat risers. Requires Vortec-specific intake manifold. Camshafts with more than 0.475 lift require machining valve guide bosses and checking valve seal to valve spring retainer clearance. Can be machined for 2.020/1.600 valves. Rocker arm studs can be pinned or drilled and tapped to 3/8. Valve spring seat diameter is 1.280. Casting number 10239906 or 12558062. This head is assembled with the following components:. 10241743 Intake Valves. 12550909 Exhaust valves. 10212811 Valve Springs. 24503856 Valve Locks. 10241744 Valve Spring Retainer. 10212810 Intake Seals. 12564852 Exhaust Seals. Additional Required Components:. Head Gaskets 10105117 (2) OR 12557236 (2). Bolts 10168525 (14), 10168526 (4), 10168527 (16). Spark Plug 19157986. Engine Application: 19258602, 19210009, 12499101, 12497317, 19210007, 19210008