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Carburetor sizes – 1 barrel The Society of Automotive Engineers developed standards for carburetor physical sizes. The more common sizes found on automobiles are listed below. Bore size is listed as approximate, as some carburetors were much more efficient than others.
Nominal ½ inch or 5/8 carburetor, center to center 1 13/16 on mounting bolts, bore size approximately 13/16 inch.
Nominal ¾ inch or 7/8 inch carburetor, center to center 2 ¼ on mounting bolts, bore size approximately 1 1/16 inch.
Nominal 1 inch carburetor, center to center on mounting bolts 2 3/8, bore size approximately 1 3/16 inch. (Often referred to as size 1).
Nominal 1 1/8 inch carburetor, center to center on mounting bolts 2 3/8, bore size approximately 1 5/16 inch.
Nominal 1 ¼ inch carburetor,center to center on mounting bolts 2 11/16, bore size approximately 1 7/16 inch. (Often referred to as size 2).
Nominal 1 3/8 inch carburetor, center to center on mounting bolts 2 11/16, bore size approximately 1 9/16 inch.
Nominal 1 ½ inch carburetor, center to center on mounting bolts 2 15/16, bore size approximately 1 11/16 inch. (Often referred to as size 3).
Nominal 1 ¾ inch carburetor, center to center on mounting bolts 3 5/16, bore size 1 15/16 inch. (Often referred to as size 4).
Nominal 2 inch carburetor, center to center on mounting bolts 3 9/16 inch, bore size approximately 2 3/16 inch. (Often referred to as size 5).
Jet size WILL have an effect on economy. Typically, 0.002 inch change in jet diameter is referred to as one size change. Although, using the words "Holley" and "economy" in the same sentence is..........................
Jon