Quadrajet Problem

[davepl]

Originally Posted by Fitz

Quadrajets are the reason I run a Holley. Never could figure one out. Must be a genetic problem or something.

And Holleys are the reason I run Quadrajets. At the track I'd run a Holley, as they're dead simple. And once you figure out all the hacks like connecting the vent tubes so you don't splooge fuel on launch, they work well.

There's a reason everything up to the the LS5 was Q-Jet; properly calibrated they run -far- better than an equivalent Holley. And I better I do not mean 1/10th at the track yet you have to drive it around with two feet so it doesn't stall when cold. I just mean driving around town.

Up until the point they exceeded the airflow of the Q-Jet GM always used them. The Corvette kept 3x2 because it was cool (except the rare LS6 I guess). Later GM adapted them to 800 cfm and so on for the big 455s, but until then the Holley was your only choice on big airflow motors.

In all honesty both will make the same power when properly calibrated (on an engine matched to their size). The Q-Jet will have better driveability, cold start, warmup driving, and pretty much everything - when properly calibrated.

Unfortunately, probably only Cliff Ruggles and three surviving engineers from Rochester can do it. And it took hundreds of hours for GM to calibrate to a specific application. And float levels vary by application - there's no "right" level for all carbs.

So that's the problem - they're so complicated to get right and so easy to screw up that eventually people pull them off and stick the old firehose 850 double pumper on it.

I can't understand why people think fuel injection is complicated - I'd rather reverse engineer the assembly code in an LS3 controller than figure out all of the systems in a Q-jet. But if someone good will do it for me, great :-)