1974 NASCAR International Stock Car Racing Rule Book NASCAR Grand National ® Championship Division Section 20-4 -- Carburetor

a. Carburetor must be NASCAR approved. Approval of carburetor shall mean approval for all competitors and cost of carburetor shall be a factor of consideration for approval. No external alterations permitted. (ACCUS). The NASCAR approved Holley 4500 Series carburetor has a 2 inch throttle bore and butterfly and was sleeved to a 1 11/16" base opening, but the 2 inch diameter at the butterfly was unaltered. The only permissible alteration is the change in the base opening size through the use of the NASCAR approved base opening insert sleeve which must conform to the specific size established by NASCAR for different design and displacement engines. Absolutely no throttle bore reduction in size permitted above the base insert sleeve. Throttle bore must remain 2 inches. No Holley 4500 Series carburetors will be permitted to be used with less than the original 2 inch throttle bore. Also, only the NASCAR approved 4150 Series Holley carburetor with a 1 11/16" throttle bore can be used. No modification permitted.

(1) Rocker arm hemispherical combustion chamber engines restricted to one four-barrel carburetor having 1 11/16" throttle bore.

(2) Overhead cam type engines restricted to one four-barrel carburetor having 1 11/16 inch throttle bore.

(3) Wedge type engines restricted to one four-barrel carburetor having 1 11/16 inch throttle bore.

(4) Engines with staggered valve design restricted to one four-barrel carburetor having 1 11/16 inch throttle bore.

(5) Intake manifold unrestricted within manufacturers line, readily available to participants. Materials optional. Internal manifold modifications are permitted.

b. Fuel injection or superchargers not permitted.

c. Jets may be any size.

d. Carburetor restrictor must be used when required by NASCAR. The 4150 and 4500 Series carburetors may be used on any approved engine. Only approved carburetors with a 1 11/16" throttle bore opening are permitted. (ACCUS).

(1) The 4500 carburetor is permitted to use only gaskets at the carburetor base.

(2) Only 2 paper gaskets (1 per side) maximum thickness .050 will be permitted on the adapter plate used with the Holley 4150 series carburetor. Only one paper gasket (.050) permitted on Holley 4500 series carburetor.

(3) Gaskets can only be altered to match carburetor base openings.

Only approved carburetors with a 1 11/16" throttle base opening are permitted and the approved carburetor cannot be altered in any manner.

e. Heat risers may be blocked.

f. Any NASCAR approved gasoline filters may be used. This applies to all late model divisions as well as speed trial and record attempts.

g. Any NASCAR approved air cleaners allowed, and they must have the complete element.