For every 'truth" there is always another side - I once owned a 350 Malibu of '73 vintage. It had a "'smogged" Quadrajet and 2.73 gears (about 4300 pounds too). Doggedy thing - but a nice riding daily driver. Mileage in town was ghastly - like 10 or 11 maybe - worse in cold weather. Specially tuned for the task, it could get 20 mpg in a flat state like Iowa or Nebraska on a summer cruise. Trouble was, in order to accelerate you had to use too much throttle - and the secondary side (even after much experimentation by a more experienced GM carb guy than me) ate up the around town mileage.
So I installed an "out of the box" Holley 6619 - with the "annular discharge" boosters (also kept the 180° manifold divided). It would then accelerate nicely in traffic -and never touch the secondaries. Mileage to work went up to 15+ and on the road she once got just over 21 for a couple of tanks that included Kansas and eastern Colorado. The carb worked fine with no tinkering required and stayed on the car for 50,000 miles - and the Chevy got changed back to the "fresh" Quadrajet when I sold it.
Fact is - the Quadrajet might have worked a little better if it had more gear to work with - but the Holley made more torque within the range allowed by the primaries and the tall rear gear. What sort of gearing is in this vehicle?
Nah - my buddy tuned the Q-jet by putting it on his 350 Nova and it worked fine with 3.23's and a thousand pounds less weight - just couldn't move the big car without tipping in all the time. His Nova carb wouldn't move it either.
The old Malibu had some legs on the top end - but had the aerodynamics of a brick.
well, my 4500 lb truck with a BBC and 3.08 gears and 28 inch tire does great with a q-jet.
I took recently off the 750 holley which was getting 8 mpg/12mpg and put on a Q-jet and got 10/15. Yes, it took some jets and rod changes and a few adjustments here and there to make it run strong. With the q-jet, I don't ever need to open the secondarys when driving around town. Smokes the tires with just a little throttle input and I'm running a LSD diff and new tires. Much more off idle torque than the holley. I have a hard time not spinning the tire off the line.
Like I said, tuning a q-jet is much tougher than a holley. q-Jet need special attention to set them up right: jets, rods, rod hangers, air bleeds, ATP, spring tensions, accel pump shaft lengths, power springs. throttle shaft bushings, ect. ect.... and a lot of times they run poorly due to crap deep inside the carb that most people don't know how to remove during a rebuild. Plus the number of rod/jet/spring combos are almost endless which greatly increases the chance of a bad setup.
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