At the risk of getting on the receiving end of the wrath of the Holley fans, GM's use of the Holley carbs was a marketing tool that had little to do with performance in the late '60s.

All performance enthusiasts in the late 50s and early 60s knew that the factory carbs of the time (AFBs, WCFBs and Rochester 4-Jets) were not performance carbs - they were cfm limited, and the way to achieve a performance gain was to install a Holley, or to run multiple carbs. That was true at the time, and Holley had the "performance" reputation that it deserved.

When introduced in 1966 on some cars, and on all GM cars in '67, the Q-Jet had no such performance reputation, even though its 750 cfm rating and excellent characteristics made it equivalent to a Holley in terms of actual horsepower numbers. The Holley still had the "magic" reputation, and GM capitalized on that by using it on their "performance" cars for as long as possible. The marketing was brilliant, and it worked. The performance crowd wanted a Holley. GM sold them a Holley. The fact that the Q-Jet could produce the same power numbers is completely irrelevant - it's marketing. GM did the same thing in later years with twin cam engines: In standard tune, you can make the same power out of a single cam engine and bigger valves, but twin cams must be performance. Rear disc brakes on passenger car sedans is another example: Your really think you need discs on the back of a Saturn? Heck it sells cars - it's marketing.

I've done quite a bit of dyno testing, and I've run Holley and Q-Jet carbs of the same cfm capacity back-to-back on the same engines. With both carbs correctly tuned and maximized for best power and air/fuel mixture, the Holley and Q-Jet (of the same size) will run virtually identical at peak power and wide open throttle. The Q-Jet will produce better torque and power at the low- to mid-range due to the smaller primary venturies and a well-refined transition circuit.

As for the Q-Jet being "an emissions carb:" GM was aware of the upcoming emissions requirements, and realized the need for a carb that could be updated and refined as the requirements emerged and became more stringent. The Q-Jet design allows the carb to be tailored for optimum efficiency through all its circuits and transitions, allowing fuel and air bleeds to be custom tailored in every circuit of the carb. The fact that the same carb design can be used and precisely set up for every GM application to meet the emissions requirements makes the carb a "well tunable" carb in my book - not just an "emissions carb." But a carb that has the capability to be well tuned with so many variables also has the capability of being really well messed up by someone altering that level of tuning... And therein comes its reputation as a "Quadrajunk" and all the other words you've heard: Any carb becomes a bad running piece of junk once its tuning has been completely messed up and altered by someone drilling out the air bleeds, drilling the IFRs, randomly changing jetting, and throwing away critical parts, such as the secondary airvalve rod.

Any properly-sized carb will run about the same as any other properly-sized carb if the two carbs are both correctly tuned. A well set up Q-Jet is pretty tough to beat - I have the test data to prove it. A badly tuned Q-Jet can run just as bad as a badly-tuned Holley, and a well-tuned Holley will run a lot better than an altered, damaged Q-Jet. Go figure...

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