Cliff's Quadrajet Parts and Rebuild Kits

General Category => Quadrajet Carb Talk and Tips => Topic started by: Marx3 on July 27, 2009, 02:07:56 PM

Title: primary/Secondary CFM-rating?
Post by: Marx3 on July 27, 2009, 02:07:56 PM

I was wondering... what is the Cfm rating om the primary side only vs on the secondary side only? for both 750 and 800 Cfm carbs... Has this ever been meazured?

Title: Re: primary/Secondary CFM-rating?
Post by: Schurkey on July 27, 2009, 02:33:12 PM

Quote from: Marx3 on July 27, 2009, 02:07:56 PM

I was wondering... what is the Cfm rating om the primary side only vs on the secondary side only? for both 750 and 800 Cfm carbs... Has this ever been meazured?

So far as I'm aware, the secondary side of the two carbs is the same.  Set 'em up equivalently--same opening angle of the throttle plate and same opening angle of the air valve--and they flow the same.

So the question is how much do the primaries flow; and the obvious answer is that the "big" primaries flow 50 CFM more than the "little" primaries.

By the way, all of the DualJets I looked at seemed to use the "800-style" venturi arrangement.  So another way to frame this question is "how much does a DualJet flow when rated as a 4-barrel carb?"

Title: Re: primary/Secondary CFM-rating?
Post by: Marx3 on July 30, 2009, 02:21:12 PM

heh, point taken, but what does a dualjet flow at 3" hg then?

Title: Re: primary/Secondary CFM-rating?
Post by: Rocky Rotella on August 17, 2009, 08:11:37 PM

This might help answer your questions.  It's from the Dec 2006 issue of HPP. 

http://www.highperformancepontiac.com/tech/hppp_0612_rochester_quadrajet_carburetor/index.html

Title: Re: primary/Secondary CFM-rating?
Post by: Schurkey on May 12, 2015, 11:42:04 PM

Blast from the past.

Found an airflow chart in a recent thread on another forum.
http://www.v8buick.com/showthread.php?296829-Checking-on-CFM-size-for-a-1974-455-2bbl

 I'm shamelessly re-posting the chart here.
(http://i172.photobucket.com/albums/w20/SLD1624/Rochester%20carbFlow_zpsa0nuiwqh.jpg)

Title: Re: primary/Secondary CFM-rating?
Post by: Ethan1 on May 13, 2015, 07:54:58 AM

Quote from: Schurkey on May 12, 2015, 11:42:04 PM

Blast from the past.

Found an airflow chart in a recent thread on another forum.
http://www.v8buick.com/showthread.php?296829-Checking-on-CFM-size-for-a-1974-455-2bbl

 I'm shamelessly re-posting the chart here.
(http://i172.photobucket.com/albums/w20/SLD1624/Rochester%20carbFlow_zpsa0nuiwqh.jpg)

 Interesting! Thank you for posting this. :D