1975 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. 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. Only the following 4500 Series model numbers will be permitted: R4575, R6214, R6464, R6605, and the Holley 4150 Series with a 1 11/16" throttle bore will be permitted for engines with displacement up to 358 cubic inches. Prototype or handmade 4500 Series carburetors not permitted. The Holley 4150 Series part number R7129 340 CFM with a venturi size of 1 11/16" and throttle bore opening of 1 7/16" is approved for large block engines from 358.001 up to 433 cubic inch displacement.

b. Carburetor spacer not to exceed 1 inch in thickness may be installed on manifold. Only 2 paper gaskets (1 per side) maximum thickness .050 will be permitted.

c. Gaskets can only be altered to match carburetor base openings.

d. Fuel injection or superchargers not permitted.

e. Jets may be any size.

f. Carburetor restrictor must be used when required by NASCAR.

g. Heat risers may be blocked.

h. Any NASCAR approved gasoline filters may be used.