OK I have to through my limited experience in here.
By far the worst experience I have had with a carb was the edelbrock. I bought the tuning kit and never could make that thing run without major bog. The older models had no way of tunning the secondary flap. I ran a Holley 3310 before that. It was cheap and rightfully so but worked all right.
My brother had his 468 stocker motor on the dyno a couple years back so we got to do some testing with it. He bought a Holley avenger. I think it was a 825. The jets needed to come up 20 points. This increased the HP by about 60.
I have a 1969 Q-jet modified by cliff that we tested also. It was within 10hp with no tuning. It was ran on the motor once just to see how it would do. Now it's on my 455.
I have read many of Cliff's post on the subject and he can typically get the numbers closer to like 2-3 hp but the Holley typically win the hp war. That being said the Q-jet with the smaller primaries can typically get better fuel mileage.
My recent expirence with the same 1969 Q-Jet and a lumpy H10 Ultradyn cam has not be good. The feul system as mention above can not keep up with the small fuel bowls so I'm changing over to 1/2 fuel line and sending unit. The low vacuum of the cam is also and issue as I have nozzel drizzel from the higher RPM and having the primaries open to far. This makes for some smelly raw gas idleing and bad looking spark plugs. I could mess with the air bypass or drill holes in the primaries but I don't want to screw up a good carb and I'm working on a roller cam install for the spring.
Some will no doubt argue with me on this but my opinion is a car that is more strip then street go with the holley. The larger feul bowls and four idle circuits makes it a good choice. If your car is more street them strip then the Q-jet with the smaller primaries gives good milage, that and the high velocity off idle performance. Where the issues seem to appear is with the larger cubic inches, larger cams over the 230 duration with tighter LSA.
Holley makes many nice carbs and the Qjets have been proven to do well over the years and no matter what you pick it will need tuning to run to its potential.
