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Quadra-Jet

The Complexity Of The Q-Jet That Makes It Such A Great Fuel Mixer May Deter Folks From Blueprinting Them For Performance

Photography by Tony Nausieda

Quadra-junk, Quadra-bog—you’ve heard them all before. Why do so many gearheads love to hate the Rochester Quadrajet? Because it’s arguably the most intricate, precise carburetor design ever produced? Because its small primary bores allow stingier fuel economy than most two-barrel carbs? Because its vacuum-operated secondary circuit ensures your engine is never over-carbureted? Because even the smallest Q-jets flow a respectable 750 cfm?

Nope, we think these name-calling skeptics just don’t understand how Quadrajets work, and more importantly, how to tune them. Most of you can probably rebuild a Holley blindfolded, but the added complexity of the Q-jet that makes it such a great fuel mixer certainly deters folks from blueprinting them for performance applications.

We recently came across a factory ’66 Buick 425ci Q-jet carb/intake assembly and thought it would make a great induction upgrade for our Carter-AFB-equipped 401ci Buick. We weren’t too happy with the 401’s current 10-11 mpg, and we felt the AFB’s 585-cfm capacity wasn’t supplying enough air to keep the big nailhead sufficiently fueled. The Q-jet’s design seemed to solve both problems; its small primaries should give us a few more miles between gas stops, and its 750-cfm capacity ought to strengthen the 401’s pathetically weak top-end charge. Even better, the induction combo would remain stock-appearing (the Q-jet was part of a rare 340hp engine upgrade for the ’66 GS). We called up JET Performance, which specializes in rebuilding and tuning the venerable Quadrajet to suit virtually any application. We took notes as JET’s resident fuel-systems guru Sean Murphy revived our tired carb—cosmetically as well as functionally.

In true Car Craft tradition, we concluded the project by installing and testing the new induction system on our GS. Not dragstrip testing, mind you, but real-world testing, by driving our beast 2000-plus miles from Milwaukee to Los Angeles. The Q-jet performed flawlessly and gave us great fuel economy and more than enough newfound passing power for the arrow-straight two-lane roads of middle America. It just may be the next best thing to EFI.

SOURCES
JET Performance Fuel Systems
Huntington Beach
CA  92647
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