The NHRA Technical Department is rescinding the Stock and Super Stock cylinder head rule changes shown below that were released in the 12/4/2019 version of the NHRA Amendments. The Stock and Super Stock cylinder head rules for 2020 will now revert back to the 2019 rules (also shown below). The Stock and Super Stock cylinder head rules will be reevaluated for the 2021 season.
RESCINDED RULES
Must be correct casting number for year and horsepower claimed, per NHRA Technical Bulletins or NHRA accepted. Porting, polishing, welding, epoxying and acid-porting prohibited. Combustion-chamber modifications prohibited. Cylinder heads are additionally restricted in that they must retain original-size valves at original angles +/- 1 degree and must be able to hold original cylinder-head volume per NHRA Specifications. Runner volumes may not exceed the current Super Stock cylinder-head volumes as listed on www.NHRARacer.com. Regardless of the poured volume measurement, any modifications to intake or exhaust runners prohibited. Any evidence of modifications from the original castings will be grounds for disqualifications as determined by NHRA in NHRA’s sole and absolute discretion. Any aftermarket steel valve permitted, must retain stock head and stem diameters. Only engines OEM-equipped with sodium-filled valves may use sodium-filled replacement valves. Titanium prohibited. Hardened keepers permitted. Lash caps prohibited. Valve-diameter tolerance: +.005-inch or -.015-inch from NHRA Specs. The following are prohibited: spark-plug adapters; any grinding in ports or combustion chambers; removal of any flashings; sandblasting or any other modification to cylinder head; any film coating of intake and exhaust runners; any film coating of combustion chamber. Runners and combustion chamber must retain OEM appearance. Final acceptance as determined by NHRA in NHRA’s sole and absolute discretion. 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. 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. Heat riser passage may be blocked from intake manifold side of cylinder head. Blocking passage down in valve pocket prohibited. The following are permitted: polylocks, jam nuts, screw-in larger-diameter rocker studs or pinned studs, bronze-wall valve guides, cylinder head studs. Valve spring umbrellas optional. Cylinder head may have all of the seats replaced. Any valve job permitted, O-ringing prohibited. Exhaust plates prohibited.
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.
2019 RULES TO ALSO BE USED IN 2020
SECTION 11A: STOCK, ENGINE: 1, CYLINDER HEADS (Page 3)
Must be correct casting number for year and horsepower claimed, per NHRA Technical Bulletins or NHRA accepted. Porting, polishing, welding, epoxying and acid-porting prohibited. Combustion-chamber modifications prohibited. Cylinder heads are additionally restricted in that they must retain original-size valves at original angles +/- 1 degree and must be able to hold original cylinder-head volume per NHRA Specifications. Runner volumes may not exceed the current Super Stock cylinder-head volumes as listed on www.NHRARacer. com. Regardless of the poured volume measurement, any modifications to intake or exhaust runners prohibited. Any evidence of modifications from the original castings will be grounds for disqualifications as determined by NHRA in NHRA’s sole and absolute discretion. Any aftermarket steel valve permitted, must retain stock head and stem diameters. Only engines OEM-equipped with sodium-filled valves may use sodium-filled replacement valves. Titanium prohibited. Hardened keepers permitted. Lash caps prohibited. Valve-diameter tolerance: +.005-inch or -.015-inch from NHRA Specs. The following are prohibited: spark-plug adapters; any grinding in ports or combustion chambers; removal of any flashings; sandblasting or any other modification to cylinder head; any film coating of intake and exhaust runners; any film coating of combustion chamber. Runners and combustion chamber must retain OEM appearance. Final acceptance as determined by NHRA in NHRA’s sole and absolute discretion. External modifications prohibited. Intake side of head may not be cut into any part of valve cover bolt holes. Valve-cover bolt holes must remain unaltered and in their original location. Intake manifold bolt holes must remain unaltered in their original location. Heat riser passage may be blocked from intake manifold side of cylinder head. Blocking passage down in valve pocket prohibited. The following are permitted: polylocks, jam nuts, screw-in larger-diameter rocker studs or pinned studs, bronze-wall valve guides, cylinder head studs. Valve spring umbrellas optional. Cylinder head may have all of the seats replaced. Any valve job permitted, O-ringing prohibited. Exhaust plates prohibited.
SECTION 12A: SUPER STOCK, ENGINE: 1, CYLINDER HEADS (Page 2)
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, intake side of head may not be cut into any part of valve-cover bolt holes (except for SS/AH). Valve-cover bolt holes must remain unaltered and in their original location. Intake manifold bolt holes must remain unaltered in their original location (except SS/AH). 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.
