Quadrajet
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==Basic design== | ==Basic design== | ||
| − | The Quadrajet is a "spread bore" carburetor; the primary [[venturi]]s are much smaller than the secondary venturis. | + | The Quadrajet is a "spread bore" carburetor; the primary [[venturi]]s are much smaller than the secondary venturis, and the center to center spacing of the throttle bores are different, primary to secondary. By comparison, a "square bore" carburetor may have primary and secondary venturis of similar if not exactly the same size and the center to center spacing of the primaries and secondaries are the same, thus the name "squarebore". |
| − | Most Quadrajets made prior to 1976 were capable of 750 [[cubic feet per minute]] (CFM) maximum air flow measured at a 1.5"/Hg pressure drop, but some were manufactured as 800 CFM. The increase in airflow was due to a larger primary | + | Most Quadrajets made prior to 1976 were capable of 750 [[cubic feet per minute]] (CFM) maximum air flow measured at a 1.5"/Hg pressure drop, but some were manufactured as 800 (and larger, in isolated cases like the '71 Pontiac H.O., more below) CFM. The increase in airflow was due to a larger primary venturi. This was first done in 1971 by the Pontiac and Buick division of GM for use on their 455 cid/high performance engines. |
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| + | In 1971 Pontiac had designed a special Q-jet that had the most flow of any production Q-jet, but because the modification decreased the vacuum signal on the primary side too much it was discontinued, so it was a "one year wonder" that fetches outrageous prices from restorers today. Many more 800 cfm Q-jets were installed from 1976-up. One way to locate a large casting carb is to source one from an '80-up light truck. Even the Chevy/GMC 4.3L V6 trucks used the large casting 800 cfm Q-jet! | ||
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