CYLINDER HEADS
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 sodiumfilled
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; cylinder-head studs; 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. Intake side of head may not be cut into any part
of valve cover bolt holes. 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, bronzewall
valve guides. Valve spring umbrellas optional. Cylinder head
may have all of the seats replaced. Any valve job permitted,Oringing
prohibited. Exhaust plates prohibited.
Forgive my ignorance but nowhere in any rulebook today or ever has it said a Stock cylinder head was legal as long as it CC'ed right on the chamber and ports. This stuff is one of the reasons I don't run stock even though I have......
In the '60 s when I first started racing Stock.....just about any cylinder head that showed up on a table in a teardown barn with some of these modifcations mentioned would have been bounced in a NY minute.......