Modified Mustangs & Fords
Dual Quad Carburetors Testing - Twin Win, Or Double Trouble? Part 1
The results of our single-four and dual-quad dyno tests on a hot 331-inch, small-block will prove surprising to some
For a long time now, we've been aware that some of the prime speed pieces of the '60s performance scene are largely missing from the current landscape. We're speaking of multiple carburetors, specifically, the dual four-barrels that were popular on everything from factory muscle cars to modified street brawlers for at least a couple of decades. As well, we'll note that when sanctioning bodies allowed, two-fours were the induction of choice for the racing set--think such disparate venues as NASCAR, Trans-Am, and NHRA drag racing. If multiple carbs were the hot ticket back in the day, why no longer?
While we still see fully restored machines with original eight-barrel induction, the modern enthusiast crowd seems to have largely moved on. Those who have done so in belief that a good single-four makes better power, may have been helped in their opinions by magazine articles in the last decade that purport the same. We can recall several tech stories in various titles that involved hot street V-8s of 350 or fewer cubic inches which, in dual-quad dress, were all blessed with at least 1,000 cfm of airflow. The results for the two-fours were 10-15 horsepower shy of a modern four-barrel setup, with the numbers always couched in a "well, it's still respectable power, and the good looks justify the penalty" attitude. Frankly, we here at MM&F find that a pretty lame perspective, yet are less than convinced the results need to be this way.
Surely the single four-barrel is a straightforward and cost effective choice, so if bang for the buck or simplicity are your priorities, it's hard to argue against it. Yet in today's market, many buyers are looking for performance and something more. It may be visual appeal, historic connection, improved driveability, improved horsepower, or a combination of all. So, do dual quads fit into this equation? They certainly do for the first two elements, but is it really true that the fabled induction will slow down a healthy street motor? If so, there's justified reason for their relative disappearance. However, with the magazine tests referred to above in mind, we're struck by the ton of cfm that 1,000 or more represents on a traditional sized small-block. Can you say over-carbureted? What about using smaller carbs on these smaller cube motors? Yes indeed!
We recently had the opportunity to test two sets of small Holley four-barrels on a healthy small-block Ford, and believe the results are enlightening. One of our parts sources is Carl's Ford Parts in Beloit, Ohio, which specializes in factory-style, multiple carb setups for a variety of vintage Ford engines. Owner Carl Binius was on board with our desire to dig into the subject, and was one of many with whom we discussed the pros and cons of multiples with. We involved racers, product reps, and speed merchants of differing backgrounds, and found advocates and pessimists alike.
But before we dig into the nitty gritty of testing dual quads, we first need to set the table by baselining a couple of popular four-barrel intakes for comparison. With this in mind, we identified two predominant schools of thought in the current '60s car hobby, one being those who are playing with real factory hot rods, or building something to accurately emulate them. Think G.T. 350. Such enthusiasts likely want to stick with the original high performance Cobra intake, or one of several others which are strikingly similar or period correct. The second group of enthusiasts is building cars without concern for originality or historical perspective, rather they're looking more toward ultimate performance, a modern appearance, and/or the best bang for the buck. In the world of current street/strip oriented single-four intakes, Edelbrock's Performer RPM has a rep for being one of the best. With this in mind, we set out to test both sides of the single-four coin by testing with a genuine S2MS Cobra aluminum high-rise from a '66 G.T. 350, followed by a Performer RPM. Holley supplied one of its new aluminum 670-cfm Street Avengers (PN 83670) as a constant for both intakes, and we were impressed by its attributes--light weight (5 pound savings over conventional Holleys), four-corner-idle circuitry/secondary metering block, quick change secondary diaphragm lid, and sparkling finish.