Dennis;
The QJet actually has a bigger window of tuning potential (for part throttle/street style use) than a Holley. Where people get into trouble with a QJet is when they take the same approach to installing/tuning one as they would a Holley, i.e. the "well, all Qjets are the same, so it should run fine" mindset. Problem is, neither the QJet
nor Holleys are all created equal, and if the wrong carb is plopped down on the wrong engine...you know what happens next.
The fact that most Holley tuning is accomplished via jets, power valve, and squirter selection whereas the QJet has a
much more sophisticated range of adjustments in as far as jets, metering rods, power piston springs, secondary air door tension spring, secondary air door vacuum break, etc. is where people start to get confused. It's actually very easy to get in over one's head when trying to tune and modify a QJet, which I am quite sure is the reason the QJet has earned such colorful euphamisms as nicknames over the years, such as "Quadra
junk", "Quadra
bog", and a few others I can't repeat on a family-oriented forum.
If you're building a non-stock hotrod and want to use a QJet, starting with a compatible core will get you 90% of the way there more often than not. It's when you try to put on a QJet designed for a `67 California smog 327 on a hot 454 that you run into problems. (I actually encountered that exact scenario recently!) Had you started with a QJet off of...say...a early `70's 454 passenger car, or even a late `70's to mid-`80's 454 truck, you would've been much better off.
OK, I'm done blathering about carbs for now.
Eric