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Installation Instructions for 51423Cylinder Heads for Small-Block Chevrolet


These Heads are Intended for Racing Use Only!!

• Heads are cast using virgin 356-A alloy material and heat treated to a T6 temper

• Combustion chamber volume: 64cc with CNC-profiled machined combustion chambers• Intake runner volume: 215cc as cast

• Intake valve: 2.100" 11/32" stem diameter, 4.960" length

• Exhaust valve: 1.600” 11/32” stem diameter, 4.960" length

• Exhaust ports are in stock location and are machined to standard bolt pattern

• Spring pocket 1.670" diameter, machined to utilize our spring cup for a 1.550"

• Premium bronze valve guides machined for .531" diameter seal

• Valve spring installed height: With .060” spring cup, you can achieve a 1.900” valve spring installed height.

• Valve seats are cast alloy designed for unleaded gasoline

• Spark plugs: Gasket-style seat, 3/4" reach with 5/8" hex.

• Custom guideplates for 5/16" pushrods are included. When installing guideplates take note that one pushrodslot is longer than the other. The longer slot is for the intake valve pushrod.

• Pushrods: Using proper length pushrods cannot be over emphasized!! Good valve traingeometry starts when the right length pushrod is used for your specific engine combination (deck height, cambase circle, lifter length and choice of rocker arms). The fact is, if you are using stock length pushrods, yourvalvetrain is probably wrong. Before ordering pushrods use an adjustable pushrod checking tool(# 270-99726-2) to determine the proper length for your particular combination. Always use heat treatedpushrods with guideplates.

• Rocker arms: Our stud location was established using standard aluminum extruded rocker arms and standardlength valves. Always trial fit rockers before final assembly! Always use a premium grade extruded aluminumroller rocker arm

• Piston to valve clearance: Most performance applications will require machining of the valve reliefs for properpiston-to-valve clearance or consider a set of custom pistons. This is a must-check operation because thevalve locations are modified and do not use stock dimensions

.• Head bolts or studs: We use stock dimension products. Check for possible guide plate and spring cupinterference. It is not unusual for large diameter valve springs to require the use of 12 point fasteners.

• Intake manifolds: There are many manifolds that do not match the flow requirements of this cylinder head. Itpays to have your manifold checked on a flowbench.

• Stud girdles: Use a stud girdle that is designed for the JEG'S cylinder heads - The valve and stud locations arenot stock OEM dimensions! Stud Girdle # 555-20505 with 7/16" adjusters was designed for this application.

• Head Gasket: Fel-Pro # 375-1010 or equivalent• Intake gasket: Fel-Pro # 375-1206 or Mr.Gasket # 720-5822 or equivalent• Exhaust Gasket: Fel-Pro # 375-1404 or Mr. Gasket # 720-5900 or equivalent• Valve jobs: When you purchase our heads bare, the valve seats extend out of the chambers and require a topcut to blend the seat to the roof of the chamber so as not to create an edge on the seat, which would promotepremature detonation.Any modification to the casting voids any warranty!

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Posted on
May 10, 2018
Instruction Guides

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