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.
