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What is the difference between AVS/AFB-style carbs
Race Director
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From: San Diego - Deep Within The State of CONFUSION!
The Carters were used on Mopar, and have four similar sized throttle bores. The Rochester Qjet GM used on hundreds of millions of cars has very large vacuum operated secondaries. It is the most misunderstood carb of all time and arguably the most common.
Tech Contributor
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From: At my Bar drinking and wrenching in Lafayette Colorado
The AFB (AFB = "Aluminum Float Bowl") carb (now touted by Edelbrock as a "performance" carb) was deemed obsolete by GM in 1966 and replaced by the more advanced Q-Jet. The Q-Jet, contrary to popular misconception, is not a vacuum secondary carb, but a mechanical secondary carb with an airvalve, and most Q-Jets flow 750 cfm. They can be tuned to an outstanding level of performance, and will typically outperform any AFB style carb once correctly set up. A new Edelbrock AFB will easily outperform an incorrectly set up Q-Jet, but this can be said for any carb comparison.
Hi Paul!!! I'm keeping my Centerline Mug full and in use at all times!
Lars
Hi Paul!!! I'm keeping my Centerline Mug full and in use at all times!
Lars
Last edited by lars; Feb 5, 2010 at 10:12 PM.
Tech Contributor
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From: At my Bar drinking and wrenching in Lafayette Colorado
The Edelbrock Q-Jets have been discontinued for about 4 years now, so you can't find a new one. The "Edelbrock" Q-Jets are genuine Rochester Q-Jets made using the original tooling under contract to Edelbrock (EDL didn't make them themselves), so there is no difference between the EDL Q-Jet and the Rochesters. The EDL carbs are the "truck" version Q-Jets, so beware that you cannot use the hi performance "passenger car" primary metering rods in the EDL integral choke carbs, nor can you use the EDL primary metering rods in your correct 1975+ Vette Q-Jet.
Lars
Lars
Race Director
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From: San Diego - Deep Within The State of CONFUSION!
Intermediate
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From: Lancaster SC
I believe it's AFB - aluminum four barrel (w/mechanical secondaries) and AVS - aluminum vacuum secondaries (w/vacuum operated secondaries). I thought they were set up like the Q-Jet w/ smaller primaries and larger secondaries. I know that they did have a AFB set made exclusivly for the super stock hemi's that had the same size barrels, spell that HUGE!!! I had a pair on a 68 hemi and found out they only made a hundred pair of them and because they were so rare, Carter didn't even have the jetting information on them anymore. Took a lot of digging to get the right info on them and boy were they some extremely thirsty carbs... never could keep any gas in that tank.
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Le Mans Master
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From: Fremont CA
Main difference between a AFB and a AVS is secondary opening, the AFB has a counterwieghted air butterfly, and the AVS has a spring loaded one as I recall from my Mopar days. The only way to adjust AFB secondary opening is by drilling weights, AVS is a turn of a screwdriver.
Also many might not know this but some very early Qjets were made under contract by Carter and have a "Carter" emblem cast into their main-bodies.
Myself, I'll stick with the crappy fuel curve of a Holley because I want to corner my Vette at high G forces. I'll save the other carbs for my pick-up truck.
Also many might not know this but some very early Qjets were made under contract by Carter and have a "Carter" emblem cast into their main-bodies.
Myself, I'll stick with the crappy fuel curve of a Holley because I want to corner my Vette at high G forces. I'll save the other carbs for my pick-up truck.
Tech Contributor
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From: At my Bar drinking and wrenching in Lafayette Colorado
Lars
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I'm sure the web site is right. I just used to teach as an instructor for the GM Training Center, and I'm sure GM had it wrong when they gave us literature showing the AFB to be "Aluminum Float Bowl" due to the one-piece cast aluminum bowl. I'll be sure to redline my GM Instructor's Manuals and change the designation.
Lars
Lars
Last edited by Project80; Feb 6, 2010 at 10:55 PM.
Tech Contributor
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From: At my Bar drinking and wrenching in Lafayette Colorado
Al Gore says AFB = "Aluminum Four Barrel" and that Global Warming is going to destroy us all. What was I thinking...??? I should throw away all factual information about everything, quit arguing "Internet Facts," and succumb to myths, notions, and popular opinion. I'll get along with a lot more people that way (very important to me, as I'm sure you've noticed).
For thought...
Both Rochester and Carter (and even MotorCraft) designated their carbs not as "barrels," but as "venturies." A 2-barrel carb was a "2V" carb, and a 4-barrel carb was technically described as a "4V." If the Carter AFB was, in fact, described as an "Aluminum Four Barrel," the designation would have been....
"A4V"...
In the meantime, I'll be building some killer stuff out in my workshop, and I hope to meet up with some of the "Internet Racers" at the local stoplights for some sporty wagers...
Lars
For thought...
Both Rochester and Carter (and even MotorCraft) designated their carbs not as "barrels," but as "venturies." A 2-barrel carb was a "2V" carb, and a 4-barrel carb was technically described as a "4V." If the Carter AFB was, in fact, described as an "Aluminum Four Barrel," the designation would have been....
"A4V"...
In the meantime, I'll be building some killer stuff out in my workshop, and I hope to meet up with some of the "Internet Racers" at the local stoplights for some sporty wagers...
Lars
Last edited by lars; Feb 6, 2010 at 10:34 PM.
Race Director
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From: Florida
Even Toyota makes mistakes 
Here is a quote from the Carter AFB Tuning Manual provided by Federal-Mogul Technical Education Center (owned Carter)
BTW, Federal-Mogul Carter sold the Carter AFB, tooling and manufacturing plant in Sanford N.C. to Magnetti-Marelli (Weber) in the late 80's. Carter and Edelbrock ran on the same assembly line.
Carter, for Federal was not worth more investment and gave up the performer afb around 10 years or so ago.
Here is a quote from the Carter AFB Tuning Manual provided by Federal-Mogul Technical Education Center (owned Carter)
BTW, Federal-Mogul Carter sold the Carter AFB, tooling and manufacturing plant in Sanford N.C. to Magnetti-Marelli (Weber) in the late 80's. Carter and Edelbrock ran on the same assembly line.
Carter, for Federal was not worth more investment and gave up the performer afb around 10 years or so ago.
Tech Contributor
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From: At my Bar drinking and wrenching in Lafayette Colorado
Good, factual info. Now we have 3 terms, "Aluminum Four Barrel," Aluminum Four Bore," and "Aluminum Float Bowl." I think we can toss out the "Aluminum Four Barrel" designation since there is no Carter/Federal/GM documentation to substantiate that one. I have the GM-provided training material in my hand that uses almost the same description as that shown in the above Carter/Federal tech paper regarding the main body design and no gaskets below the fuel level, but it uses the term "Aluminum Float Bowl" to describe the AFB designation for this reason. It was published in 1972, and carries GM and Carter logos - there is no Federal/Mogul endorsement on this 1972 document, making it quite possible that the acronym designation was altered between the 60's and the time that Fed/Mogul got involved. Noonie - is there a date on your document? Would be interesting to see if there was an evolution in the acronym or if GM and Carter used different terms for the same carb.
Lars
Lars
Team Owner
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From: Orange Park Florida
Good, factual info. Now we have 3 terms, "Aluminum Four Barrel," Aluminum Four Bore," and "Aluminum Float Bowl." I think we can toss out the "Aluminum Four Barrel" designation since there is no Carter/Federal/GM documentation to substantiate that one. I have the GM-provided training material in my hand that uses almost the same description as that shown in the above Carter/Federal tech paper regarding the main body design and no gaskets below the fuel level, but it uses the term "Aluminum Float Bowl" to describe the AFB designation for this reason. It was published in 1972, and carries GM and Carter logos - there is no Federal/Mogul endorsement on this 1972 document, making it quite possible that the acronym designation was altered between the 60's and the time that Fed/Mogul got involved. Noonie - is there a date on your document? Would be interesting to see if there was an evolution in the acronym or if GM and Carter used different terms for the same carb.
Lars
Lars
I wonder what Mopar folks say on that point....I dunno where to look...
I just remember seeing a Hemi with dual quads on it AFB's....and the cross ram 413? engine, an old Mopar buddy had a set of the cross ram induction all polished up and setting on his coffee table....
Race Director
Joined: Mar 2006
Posts: 14,112
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From: Florida
Good, factual info. Now we have 3 terms, "Aluminum Four Barrel," Aluminum Four Bore," and "Aluminum Float Bowl." I think we can toss out the "Aluminum Four Barrel" designation since there is no Carter/Federal/GM documentation to substantiate that one. I have the GM-provided training material in my hand that uses almost the same description as that shown in the above Carter/Federal tech paper regarding the main body design and no gaskets below the fuel level, but it uses the term "Aluminum Float Bowl" to describe the AFB designation for this reason. It was published in 1972, and carries GM and Carter logos - there is no Federal/Mogul endorsement on this 1972 document, making it quite possible that the acronym designation was altered between the 60's and the time that Fed/Mogul got involved. Noonie - is there a date on your document? Would be interesting to see if there was an evolution in the acronym or if GM and Carter used different terms for the same carb.
Lars
Lars
The FM manual I have has no dates, but must be after '85 or therabouts when Federal-Mogul aquired Carter from ACF Industries, the parent company. FM had a huge history in the 70's and 80's of buying automotive suppliers.
Carter also included the term "downdraft" since they also made updraft and what they called "horizontal" carbs (what we mostly know as "side draft").
