The Rochester Quadrajet was General Motors’ carburetor for dependable, performance four-barrel applications for almost 20 years. While other types of carbs have enjoyed much success on modified engines, the Q-jet can be altered and tuned to also perform well on even the most demanding powerplants. We’ve even heard of them being used on blown engines!
The latest news in Q-jet circles is that Edelbrock now makes a Performer original equipment (O.E.) replacement series carburetor for Q-jet applications. These spread-bore carbs are manufactured by Weber, USA, and are stock replacement parts for Chevrolet and GMC vehicles for which the Q-jet was available originally. The advantage of the Edelbrock Q-jet over a used original is that it is brand new. Nothing is broken, missing or warped. There is no guessing involved in purchase, and everything works like it’s supposed to. While the carbs perform well as replacements right out of the box, they can be tuned up for even better results.
That’s where The Carburetor Shop comes into play. It has been known for making seasoned Q-jets run at their best, so we gave the company’s technicians a stab at a new one. Besides commenting that it is really nice to work on a new, clean carburetor for a change, The Carburetor Shop felt right at home upgrading the familiar unit.
The new Edelbrock carb we brought to The Carburetor Shop was custom tailored for a small-block Chevy engine that makes 450 horsepower. The Carburetor Shop took into consideration specific engine components, transmission type, torque-converter stall speed, vehicle weight and rear axle gear ratio.
The Carburetor Shop also pointed out that while we used an early-style 750-cfm Q-jet (Edelbrock part No. 1901), a later-style 795-cfm model (Edelbrock part No. 1904) probably would have been better for our application. Not only is it rated at a higher cfm capability, but it has an electric choke. Also, the adjustable part-throttle can be accessed through the carb top rather than through the baseplate.
When The Carburetor Shop was finished, the flow bench showed a definite increase in cfm over stock. Of course, we don’t drive flow benches, so the carb was bolted onto our 450hp engine for a spin around the block. The idle was much improved, as was part-throttle response. Seat-of-the-pants evaulation showed that the carb helped bottom-end torque, and the throttle transitions seemed to be smoother.
The Edelbrock carb worked well, and not having to correct years of abuse and wear was nice. The Carburetor Shop improved on the piece by fine-tuning the individual air and fuel circuits for an application for which the carb was not intended stock.
