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Old 07-29-2013, 03:11 PM
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Originally Posted by rogus View Post
can anyone tell me if the quadrajet ever came in a size smaller than 750 cfm? If so how do you tell the cfm rating? i am looking for something around 550 cfm for a recently rebuilt 350 sbc.
Q-jets came in two basic castings, 750 cfm and 800 cfm. The difference is in the size of the primary venturi (shown below). There was a one-year-only Pontiac carb ('71 IIRC) that had a booster ring removed from the primary side that added a bit more flow- at the cost of off idle response. This wasn't used again in production Q-jet carbs.

You can restrict the flow of any Q-jet easily enough. This can be done by adjusting the air valve stop and/or the secondary throttle butterflies to not open fully. That said, you can tailor a Q-jet to work perfectly well on a mild 350 sbc w/o worrying about the cfm. The Q-jet was used on the Chevy V6 4.3L engines in trucks- and most of these carbs had the bigger 800 cfm castings, believe it or not.

If you have the carb number, I can give you a good baseline to work from.

More on the Q-jet here and here.

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