Quadrajet Casting Number Chart

Tag showing Quadrajet ID on an early Quadrajet Quadrajet Numbers Through the years of production, the manufacturer used numbers for carburetor identification. Very early Quadrajets had tags installed into a cast round area on the drivers side of the main body.   In and after about 1968, stamped numbers were used for identification. The large flat area on the main body just above the secondary throttle shaft has a series of numbers stamped into the casting. In most cases these numbers can be used to identify the year and application the carburetor was originally used on. Quadrajet Carburetor Numbers 68 and later Identify …

Quadrajet History and Design

SUMMARIZED FROM THE BOOK:“HOW TO BUILD AND MODIFY ROCHESTER QUADRAJET CARBURETORS”BY CLIFF RUGGLES The Rochester Quadrajet was a standard production four-barrel carburetor used by every General Motors division for nearly 20 years. Although it never deviated far from its original basic design, the Quadrajet underwent several modifications over the years, proving its versatility over a wide variety of applications. From a practical standpoint, most Quadrajets were never intended to be “high-performance” carburetors. General Motors produced vehicles for a very broad customer base, and each division developed its own engines. Since many different engines were offered in a wide variety of vehicles, nearly every carburetor …

Electric Choke Q-Jets

Any carburetor originally equipped with a hot-air-style choke can be converted to an electric choke in minutes. The vacuum supply to the housing must be blocked off and the gasket under the choke discarded because the unit uses the housing as a ground. The Quadrajet saw expanded use onto a wide variety of 1966 Chevrolet V-8 and Buick 400 and 425 V-8 cubic-inch engines in 1966. Oldsmobile followed suit. By 1967 Cadillac and Pontiac too had begun installing the Quadrajet on most of their 4-barrel applications. With its growing popularity and efficient design, the Quadrajet was the most widely used …

Quadrajet Model Designation Descriptions

Although many castings are referred to by specific characteristics such as airflow capacity or choke type, Rochester actually gave each Quadrajet style different designations indicating body type and choke style. The first design series was designated 4M and can be found on all GM vehicles through 1974 and on GMC and Chevy trucks through 1977. When Rochester redesigned the Quadrajet in 1975, they referred to it in factory literature as the “Modified Quadrajet” or “Mod-Quad,” and designated it M4M. When computer-operated electronic internal components were added around 1980, Rochester designated the Electronic Quadrajet the E4M. The last letter in the series designation generally indicates …

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