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Carburetors Carb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.

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Old 02-17-2007, 08:33 PM   #1
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Car: 1987 IROC-Z Camaro
Engine: 5.7 350 TPI - SLP Runners, AFPR, MSD Goodies
Transmission: 700R4 - Shift Kit, Corvette Servo
Axle/Gears: BW 9 bolt, 3.27s

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quadrajet cfm?

Just curious, how much cfm is the stock quadrajet carb rated at? It came off an 86 sport coupe 305. I have a 650dp on the car, but one of the bowls was leaking so i yanked it off and put one of those on there so I can drive it around until my new bowl comes in. My guess is around 500cfm.
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Old 02-18-2007, 12:50 PM   #2
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Not sure of the 'exact' cfm flow rating on the LG4's (some of the 80's quadrajet's flowed as much as 850-cfm). I'm pretty sure the LG4's flow more than 500-cfm, though....

Jeez, I remember those days. Trying to mate a CC-Carb with a ECM-less engine. Removing the stock idle mixture screws, I mean plugs (lol), then making a 'slit' in them with a hacksaw to be able to turn them with a screwdriver. Oh yes, fun, fun times...
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Old 02-18-2007, 05:03 PM   #3
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Car: 1987 IROC-Z Camaro
Engine: 5.7 350 TPI - SLP Runners, AFPR, MSD Goodies
Transmission: 700R4 - Shift Kit, Corvette Servo
Axle/Gears: BW 9 bolt, 3.27s

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it was a pain, but the car was originally an lg4 car and I left all the plugs and harness in the car and tucked them in my a/c airbox, i pulled it off and connected everything. I have to say, compared to my double pumper this carb sucks lol but it works.

the motor is a 406 with a choppity chop cam and all that jazz in case you were wondering
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Old 02-18-2007, 10:46 PM   #4
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Most books state there were two size Q-Jets made, I have run across two different sized Q-Jets after looking at a couple hundred. They were rated at 750 or 800 cfm. I have also seen articles where guys have flowed tested them and had figures of 700-850 cfm.
The primary holes are the difference by I believe 1/16 th in. It isn't much and if you didn't have them side by side to see the difference it would be tough to tell which one you had unless you know what to look for.
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Old 02-19-2007, 01:54 PM   #5
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There were only 2 basic castings for the QJet- 750 CFM and 800 CFM, the difference between the two being in the primary venturi diameter. Everything computer controlled was built off the smaller 750 CFM casting that I've ever run into. That's not to say that they actually flow than much from the factory- the secondary air valve is often limited to only ~70* of opening, rather than the ~90* you'd need to get the full 750 CFM from the carb.
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Old 02-19-2007, 01:54 PM
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