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Old 07-08-2006, 10:35 PM   #1
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does anyone know if quadrajets have cfm ratings or are they all the same?
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Old 07-08-2006, 10:37 PM   #2
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Old 07-09-2006, 07:21 AM   #3
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did they make 750 cfms?
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Old 07-09-2006, 08:39 AM   #4
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there are many variations of the Q-jet,one way to tell is if the fuel line turns to the side it's more that likely a 635cfm and if the fuel line runs strait out the front it a 750cfm carb.if you can find one with an extra vent tube that sticks up through the air cleaner base in the front it's an 800cfm carb.

just about all Q-jets can be tuned for 750cfm or more with the right adjustments,jets,metering rods,air dashpots and flap spring adjustments.
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Old 07-09-2006, 09:11 AM   #5
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http://cgi.ebay.com/ebaymotors/ws/eB...K%3AMEWA%3APIC
does this carb look like a 750?
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Old 07-09-2006, 10:43 AM   #6
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There's no way to tell without looking at them. You will have to get the part number off of it to see what it came off of. The number should start with a 7 or 17, the later ones used the 17 numbers.

I havent ever heard of a q-jet smaller than 750, and the little bit of research I just did online only mentions 750-800. The 750s were typically used on small blocks and 6 cylinders, the larger 800 was found mostly on big blocks.

As far as the different fuel inlets, I believe it was more of a year model/carb style thing. From what I have seen, the older models used the straight inlet while the newer ones had the inlet facing the pass. side.

The main thing to look out for on a q-jet is loose throttle shafts. The shafts are steel and the throttle plate is aluminum. As a result the softer aluminum holes egg out over time. The bigger holes cause vacuum leaks and can cause performance problems. I havent seen too many quadrajets that didnt have the holes egged out. Just keep in mind that the newest factory carb is 16 years old.

Also watch out for the electronic carbs. They were mostly on mid-late 80s cars, but I have seen a few on trucks too.

Here's a little info about q-jets. http://carbs.partschoice.com/tech/Ro...jet-index.html
More can be found if you do a web search.
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Old 07-09-2006, 05:00 PM   #7
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Zach if you read that again it says"no more than 750-800 cfm" but you are right on with this,its really all in the application it was set up for.

have you ever seen a Duel-jet?it's a 2 barrel version of the Q-jet. these work great in off camber and vertical.
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Old 07-09-2006, 05:42 PM   #8
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Quote:
The QJet is a large 4 barrel carburetor that has a small primary side for fuel economy and good emissions and a large secondary side for good performance. QJets have a maximum airflow of from 750-800 cfm. Because the secondary side of the Qjet opens according to the airflow requirements of the engine, the same basic carburetor size can be used on a large range of engine sizes. The basic 750 cfm QJet casting is used from 231 CID to over 400 CID - the big secondary air valves open only as the engine breathes For example, on a mild 350 Chevy the air valve will never open all the way - because the motor can't use more than 600 cfm or so.
What it actually says.
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Old 07-17-2006, 10:03 AM   #9
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Originally Posted by texasfrog
Zach if you read that again it says"no more than 750-800 cfm" but you are right on with this,its really all in the application it was set up for.

have you ever seen a Duel-jet?it's a 2 barrel version of the Q-jet. these work great in off camber and vertical.
What can you tell me about the dual jet?

That may be a good solution, especially if it works as well as a Q jet. It's gonna be hard to top the ole Autolite 2100 though for a good 2 barrel.
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