Stock eliminator heads..........
CYLINDER HEADS (April 15, 2013)
ENGINE
Must be same year and make as car used, aftermarket NHRA-
accepted cylinder blocks permitted. Equipment other than original
factory-installed prohibited. Any special equipment export kit
(superchargers, dealer-installed options, etc.) automatically
disqualifies car. Engine must remain in stock location — height,
setback, etc. Cylinder bores must not exceed .080-inch over stock.
Bores are measured at top of cylinder where ring wear is not
evident. Crossbreeding parts prohibited. Normal balance job (i.e.,
one piston/rod assembly untouched) permitted. Otherwise
lightening of component parts prohibited. All carburetors, manifolds,
heads, etc. must be tightened to prevent any air or fuel leaks.
Vacuum lines must be securely connected or blocked off. Stroke
tolerance is +/- .015-inch. Stock OEM or NHRA-accepted
aftermarket crankshaft mandatory. Aftermarket crank must retain
OEM configuration (i.e., billets, knife edging, etc. prohibited).
Lightening of crankshaft other than normal balance job prohibited.
Cylinder blocks may be sleeved. Aftermarket SFI Spec 18.1
harmonic balancer mandatory in AAA/S through G/S and AAA/SA
through G/SA. See General Regulations 1:2.
SUPERSEDED AND/OR REPLACEMENT PARTS
Superseded parts are restricted to cylinder heads, intake manifold,
crankshaft, cylinder block, and transmission only when
manufacturer lists such parts in its published parts book, notifies
NHRA of said change, and change is accepted by NHRA.
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; 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. 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.
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.
Valve spring umbrellas optional. Cylinder head may have all of the
seats replaced. Any valve job permitted,O-ringing prohibited.
Exhaust plates prohibited.