When introduced it was the most complicated carburetor of its time, incorporating four-barrels and many functions (i.e. fast idle, choke). It was a fearsome rebuilding task for most technicians who were used to tuning Holleys and Carters. The myriad of linkages, internal circuits, and easily lost tiny pieces were incomprehensible to some. With age the Quadrajet earned a following of techinicans who understood its design and recognized its potential.
The primary barrels of the carburetor are tiny compared to most four-barrel designs, but this is what gives the Quadrajet its gas mileage edge. In contrast, the secondary barrels are huge, providing a performance edge. During normal driving the primary barrels are adequate for cruising speeds. The beast comes out when the pedal is depressed further. The secondaries open and there is the slightest amount of delay as the accelerator pump richens the mixture. A Quadrajet carbureted car is often distinguishable from other cars by the sound of the engine as the secondaries open. There is a moment of quiet followed by a large increase in exhaust volume, sometimes described as a 'booming' noise.
Most performance enthusiasts shun the Quadrajet as a stock carburetor laden with useless emissions controls. In reality the Quadrajet offers performance on par with most aftermarket carburetors while retaining good driveability and gas mileage. With a little modification most Quadrajets can easily reach 750CFM airflow.
There were many iterations of the Quadrajet, even including some electronic versions produced while General Motors was dragging their feet in changing to electronic fuel injection. The most desirable are the ones installed on '71 to '78 Cadillac, Buick, Oldsmobile, and Pontiac big-block powered high-performance and luxury cars. These flow 800CFM in the stock configuration. There is also a rare 840CFM version that was installed on '73-'74 Pontiac Super Duty 455s.
Last paragraph corrected with information from the July 2000 issue of Hot Rod Magazine.