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NHRA Announces Updated Super Stock Cylinder Head Rules

After working closely with the Stock and Super Stock Sportsman Racers Advisory Council, the NHRA Technical Department is releasing the new Super Stock cylinder head rules. The rule amendment below can also be found in the NHRA Rule Amendments located on NHRARacer.com. 

SECTION 12A: SUPER STOCK, ENGINE: 1, CYLINDER HEADS (Page 2) (12/4/2019) (1/28/2020)

Must be correct casting number for year and horsepower claimed, per NHRA Technical Bulletins or NHRA-accepted. Cylinder-head casting must also be on NHRA runner volume list as published on NHRARacer.com. Porting, polishing, welding, epoxying, and acid-porting permitted. Grinding and polishing in combustion chamber permitted. Welding and/or applying epoxy in combustion chamber prohibited. Spark-plug hole must maintain the stock location, size, and angle as machined by the OEM; spark-plug adapters prohibited. Valve-guide centerlines must maintain the stock lateral and front-to-back location as machined by the OEM. Valves must maintain stock angle; valve- stem angle must remain stock, +/- 1 degree. Cylinder head must be able to hold combustion chamber, intake and exhaust runner volumes per NHRA Specifications. Any aftermarket steel valve permitted; must maintain stock head and stem size; titanium valves prohibited. (OEM sodium-filled valve may be replaced with titanium, provided weight is equal to or greater than original.) Valve diameter permitted to be +.005-inch or -.015-inch from published NHRA Technical Bulletins. Angle milling of cylinder head, exhaust and intake mating surfaces permitted. Valve-cover bolt holes must remain unaltered and in their original location. Intake manifold bolt holes must remain in their original location (except SS/AH). Additional intake manifold bolts holes permitted. Spacer plates between intake manifold and cylinder head permitted. Welding or epoxying permitted on external portion of runners for repair only, maximum 2 runners per head. Heat riser passages may be blocked off from intake-manifold side of cylinder head or in exhaust port. The following are permitted: cylinder head studs, polylocks, jam nuts, screw-in or pinned studs. Any valve job accepted. Exhaust plate permitted between header and cylinder head, maximum 1/2-inch; may not protrude into exhaust port. Cylinder head may have all seats replaced.                 

 

Must be correct casting number for year and horsepower claimed, per NHRA Technical Bulletins or NHRA-accepted. Cylinder-head casting must also be on NHRA runner volume list as published on NHRARacer.com. Porting, polishing, welding, epoxying, and acid-porting permitted. Grinding and polishing in combustion chamber permitted. Welding and/or applying epoxy in combustion chamber prohibited. Spark-plug hole must maintain the stock location, size, and angle as machined by the OEM; spark-plug adapters prohibited. Valve-guide centerlines must maintain the stock lateral and front-to-back location as machined by the OEM. Valves must maintain stock angle; valve- stem angle must remain stock, +/- 1 degree. Cylinder head must be able to hold combustion chamber, intake and exhaust runner volumes per NHRA Specifications. Any aftermarket steel valve permitted; must maintain stock head and stem size; titanium valves prohibited. (OEM sodium-filled valve may be replaced with titanium, provided weight is equal to or greater than original.) Valve diameter permitted to be +.005-inch or -.015-inch from published NHRA Technical Bulletins. External modifications prohibited except for the following, intake side of head may be +/- 2 degrees from OEM angle between combustion chamber surface to intake flange surface, may not be cut into any part of valve-cover fastener holes (except for SS/AH). Intake manifold fastener holes must remain unaltered in their original location. Only OEM intake fastener holes are permitted, any additional fastener holes are prohibited. Spacer plates between intake manifold and cylinder head prohibited. Valve-cover fastener holes must remain unaltered and in their original location. Welding or epoxying permitted on external portion of runners for repair only, maximum 2 runners per head. Heat riser passages may be blocked off from intake-manifold side of cylinder head or in exhaust port. The following are permitted: cylinder head studs, polylocks, jam nuts, screw-in or pinned studs. Any valve job accepted. Exhaust plate permitted between header and cylinder head, maximum 1/2-inch; may not protrude into exhaust port. Cylinder head may have all seats replaced.

 








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