What carb size mopar 340.

[540HemiCuda]

You do realize that the choke is manually controlled and often does not need to totally seal the venturies while the air door must be able to respond on it's own hence the basic design difference. But is it your position that neither the choke nor the secondary air valve exerts any more pull on the boosters by resisting air flow? If so, you are just plain wrong.

And again, if the air door is not designed to enrichen the secondary's opening point, why don't double pumpers have them, too? ONLY mechanical secondary carbs with no other means to add fuel at that point have them. Why is that?

And your quote does nothing to sway the argument either way.

Here is what AI says: '
The air door, or air valve, on mechanical secondary carburetors (specifically Air Valve Secondary or AVS type) serves to gradually open against spring pressure, controlling airflow and creating a sufficient air velocity to draw fuel from the secondary boosters. This system prevents a lean stumble or "bog" when you stomp on the accelerator at low RPMs, ensuring smooth power delivery by allowing the carb to only add fuel when the engine demands it through sufficient airflow.

The air valve's position controls the airflow through the secondary venturi, creating the necessary velocity to generate a fuel signal from the secondary boosters. Without this system, the secondary throttle plates would open too quickly, causing too much air to enter without enough fuel, resulting in a lean condition or a "bog" '

Or this from a carburetor shop:
'Even if the throttle plates open fully, the secondaries won’t deliver extra fuel unless enough air velocity flows through the secondary side to push open that air door. This prevents bogging or lean conditions when stomping the throttle at low RPMs.
As the air valve opens due to increasing airflow, it activates the fuel metering rods and jets in the secondary side.'

Lots more information about this if you chose to do a search.

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[Xcudame]

Find a good used Thermoquad and rebuild it. Can't find one, get a Holley Street Demon.
@Chryco Psycho is on the money, 2x the cubic inch of the engine.

 

[Litchkar]

I don't know what parts manual you are using, but it is INCORRECT.

And I am not going by anything other than 55+ years of personal experience. Starting in 1972, I have had over two dozen Mopars, sometimes as many as 4 at once. Some stock, some modified. I can list them off for you if you would like. I am now down to just one, a '70 HemiCuda with a 540" Hemi which I built myself like all my engines. And just to throw one last point on my resume; I built a '71 GTX in 2000 (which still had it's original Carter AVS with mechanical secondaries by the way) and it was awarded 95 points out of 100 at the 2001 Mopar Nationals which earned it O.E. Certifed status. So, don't accuse me of using anything other than personal experience especially when you so obviously lack that yourself.

Have you never heard of the Carter AVS? Or the Carter Thermoquad? Both are mechanical secondary carbs, and were standard equipment on just all high performance Chrysler single four barrel applications. And before those, the standard four barrel carbs were the Carter WCFB and the AFB both of which are also, mechanical secondary carbs.

And since you brought up AI, even AI knows that you are incorrect. Google up the carb application for a hi performance 340, 383, or 440. Or you can go to a source like Mopar Muscle magazine where this excerpt on Mopar carbs came from:

'The most common four-barrel carb found on Chryslers during the '60s era were manufactured by Carter and came in two specific designs: the AFB (Aluminum Four Barrel) and the AVS (Air Valve Secondary). From a distance, the two look virtually identical; both are box-like in shape and use a quadrant of evenly or almost evenly sized barrels when viewed from the bottom.

After the WCFB was discontinued, the single AFB was the standard carb on Chrysler performance models until the debut of the AVS in 1968. The specific date code and four-digit part number on both the AFB and the AVS models are easily visible in front of the passenger-side mounting flange.'

http://[URL]https://www.hotrod.com/how-to/mopp-0111-chrysler-oem-carburetors

[/URL]

Seems EVERYONE (except you) knows what carbs came on most of Mopar's hi performance engines.

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I don't know what parts manual you are using, but it is INCORRECT.

And I am not going by anything other than 55+ years of personal experience. Starting in 1972, I have had over two dozen Mopars, sometimes as many as 4 at once. Some stock, some modified. I can list them off for you if you would like. I am now down to just one, a '70 HemiCuda with a 540" Hemi which I built myself like all my engines. And just to throw one last point on my resume; I built a '71 GTX in 2000 (which still had it's original Carter AVS with mechanical secondaries by the way) and it was awarded 95 points out of 100 at the 2001 Mopar Nationals which earned it O.E. Certifed status. So, don't accuse me of using anything other than personal experience especially when you so obviously lack that yourself.

Have you never heard of the Carter AVS? Or the Carter Thermoquad? Both are mechanical secondary carbs, and were standard equipment on just all high performance Chrysler single four barrel applications. And before those, the standard four barrel carbs were the Carter WCFB and the AFB both of which are also, mechanical secondary carbs.

And since you brought up AI, even AI knows that you are incorrect. Google up the carb application for a hi performance 340, 383, or 440. Or you can go to a source like Mopar Muscle magazine where this excerpt on Mopar carbs came from:

'The most common four-barrel carb found on Chryslers during the '60s era were manufactured by Carter and came in two specific designs: the AFB (Aluminum Four Barrel) and the AVS (Air Valve Secondary). From a distance, the two look virtually identical; both are box-like in shape and use a quadrant of evenly or almost evenly sized barrels when viewed from the bottom.

After the WCFB was discontinued, the single AFB was the standard carb on Chrysler performance models until the debut of the AVS in 1968. The specific date code and four-digit part number on both the AFB and the AVS models are easily visible in front of the passenger-side mounting flange.'

http://[URL]https://www.hotrod.com/how-to/mopp-0111-chrysler-oem-carburetors

[/URL]

Seems EVERYONE (except you) knows what carbs came on most of Mopar's hi performance engines.

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I see you are new to the site, being knowledgeable is great, but insulting fellow members is not cool. People use this forum to ask and answer questions, not be belittled. Grow up and show some respect.

 

[Rishi]

He is just being reactive, like my teenage son.

while it may be true the secondaries on the AVS and TQ share a mechanical element with the AFB, I don’t agree they behave like the AFB.

the spring controlled valve improves their tuning as a function of engine demand, and it does so at a very tiny cost in performance, possibly not even measurable. In many ways, the secondary opening speed behaves very similar to the Holley vacuum secondaries.

they’re both right, from some schools of thought. but boys, will be boys.

 

[Ricks72Chlgr440]

He is just being reactive, like my teenage son.

while it may be true the secondaries on the AVS and TQ share a mechanical element with the AFB, I don’t agree they behave like the AFB.

the spring controlled valve improves their tuning as a function of engine demand, and it does so at a very tiny cost in performance, possibly not even measurable. In many ways, the secondary opening speed behaves very similar to the Holley vacuum secondaries.

they’re both right, from some schools of thought. but boys, will be boys.

I my mind I always equated mechanical secondaries with those Holley carbs that had dual squirters. Does not make me correct but that's how I run.

 

[540HemiCuda]

I see you are new to the site, being knowledgeable is great, but insulting fellow members is not cool. People use this forum to ask and answer questions, not be belittled. Grow up and show some respect.

What exactly was an insult? I corrected an obvious mistake and responded to being accused of using AI rather than my experience which I consider an insult. In essence, I disagreed, offered support for my position, and asked a couple of questions that cut directly to the point but went unanswered.

I look at it as a challenge that was met. Successfully.

 

[Xcudame]

I like to look at it like this. First there were two barrel carburators and Will Carter made the first Aluminum Four Barrel known as the AFB. Used on all the Big Three performance cars. Then Carter came out with the AVS (air valve secondary) that used engine vacuum to determine how much flow and fuel would go through the secondaries instead of the secondaries being totally mechanical. Holley and other makes followed suit. Next came the awesome Thermoquad. Except for a brief stint with the Chevy Rochester (saved a few cents per car over the Thermoquad), Chrysler went to throttle body fuel injection and then multi-port fuel injection. Kinda like an evolution of fuel delivery. Properly tuned for the engine, any carb will work. The great thing about the AVS and Thermoquads are that you can dial one in on a 440 and then put it on a 318 (corresponding intake manifold) and it would run great. Where as the mechanical secondary carbs really need to be tuned to the engine they're on and more than likely won't work on another engine of different displacement.

No artificial intelligence is going to replace oily hands and scrapped knuckles!!

 

[pschlosser]

@Xcudame you rock, my man.

 

[540HemiCuda]

History lesson aside, you did not attempt to answer the basic questions I asked, so I will try once again:

A)Why is the air valve ONLY used on carbs with mechanical secondaries and no other secondary enrichment? Why aren't they on ANY double pumper? Why wouldn't they work the same on them?

B)And are you saying that having an air restriction ABOVE the boosters does not cause additional pull on the boosters? Like say a choke? Or an dirty or undersized air cleaner? Why don't they all have the same effect?

C)How does an air valve magically control the volume of air without causing more pull on the boosters and therefore a richer mixture like any other air restriction ABOVE the boosters?

D)Why does an air valve act different than a choke plate? A choke restricts/controls the amount of air entering the primary and thereby is an enrichment device, but the same thing on the secondaries does something different?

We call the AFB a mechanical secondary carb because the secondaries are operated mechanically. The secondaries on the AVS are operated the same EXACT way. Having an air door or valve ABOVE the venturies does not change how the secondaries are opened.

The air valve was introduced when the secondaries became large enough to need additional enrichment when opened before the engine was really ready. It does control air flow, just like a choke. And for the same reason. Secondary enrichment. Now if the carb is terribly oversized, there could be other side actions as well. But while that may apply to the huge secondaries on the Thermoquad, the same cannot be said for the AVS.

The air valves on mechanical secondary carbs are there PRIMARILY as an enrichment device. Which is why you have NEVER seen any on double pumpers.

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[Xcudame]

Buy, read and learn. There are similar books for Holley carburators. Also, you need to understand an engine is basically an air pump and can only "suck" in so much air. The ram effect can force more air in (as can turbos), but with natural aspiration, only 85% to 95% of an engine's cubic displacement is going to get into the engine. The advantage of air valve secondaries is the engine's "sucking" controls how much air gets through the secondary air valve and a corresponding amount of fuel is sucked out of the secondary boosters.

Don't get me started on Holley double pumpers! Great for a full on race car, but totally suck on the street for everyday driving!

 

[pschlosser]

you did not attempt to answer the basic questions I asked

some find it best to not feed the trolls

 

[540HemiCuda]

Buy, read and learn. There are similar books for Holley carburators. Also, you need to understand an engine is basically an air pump and can only "suck" in so much air. The ram effect can force more air in (as can turbos), but with natural aspiration, only 85% to 95% of an engine's cubic displacement is going to get into the engine. The advantage of air valve secondaries is the engine's "sucking" controls how much air gets through the secondary air valve and a corresponding amount of fuel is sucked out of the secondary boosters.

Don't get me started on Holley double pumpers! Great for a full on race car, but totally suck on the street for everyday driving!

View attachment 146242

I have Emanuel's Holley book. As well as the Walordy Holley book. And I think I still have an old Edelbrock tuning guide.........somewhere.

Frankly, I haven't spent much time with Thermoquads the last 40 years or so. Simply because there are too few parts available (in particular tuning parts), too few quality units left, and better choices have been introduced since they have been discontinued. Actually, I think I still have one or two in a parts bin...........somewhere.

The ONLY real application nowadays (with the wide selection of better carbs available) for any Carter is an original, stock carb on a resto type deal or a stock class restriction. The CarterBrock style of carb primarily suffer from 2 distinct disadvantages A) lack of tuning flexibility especially in the transitions, and B) lack of ready access to tuning parts. And that goes DOUBLE for the Thermoquads.

And you still haven't touched on why double pumpers have never had secondary air valves. Or why restricting the air above the boosters with an air valve does not result in a richer mixture. You know, like a choke does.

I totally agree that for those who are not familiar with Holley carb tuning that double pumpers are a poor choice for the street and is not something I have recommended here. They are tuned for the track out of the box. But the really good thing about the 4150 platform is it's incredible flexibility when it comes to tuning along with those tuning parts being readily available EVERYWHERE. Even my local O'Reilly's stocks some pieces and can have most everything else that afternoon or the next day. Try that with ANY Thermoquad tuning parts. Or almost any CarterBrock tuning parts for that matter. And by the way, in capable hands, a little tuning with a wide band and the double pumpers can run as clean on the street as any 'street' oriented carb. Been there, done that.........many times

And I disagree with your assertion that naturally asperated engines cannot achieve 100% volumetric efficiency. In fact, they can and do EXCEED 100%. You won't believe me but do a little research. Or you can provide information to PROVE your assertion.

Your examples are all about using a carb that is too large for the application rather than being sized for the application. Do you ALWAYS recommend an oversized carb with an air door? What are the indicators that an air door is required? When are they not required, in your opinion?

And I would be remiss if I did not point out that engines DO NOT SUCK. They only allow barometric pressure to push air into the engine. Hence, the desire for 'mine shaft air' when looking for the best E.T. and MPH possible. The higher the barometer, the more air that the engine can get and the more oxygen that is in that air.

So, enlighten me: How many carbs have you tuned with a wide band? How many Mopar 6bbls have you worked the bog out of or dialed in the opening point? How many 4500 Holleys have your converted to street use or converted 3 circuit to 2 circuit? How many double pumpers have you tuned to be lean and mean for street use? How many good old 3310s have you made to work really well and drive clean?

Ask me those same questions AFTER you answer them.

You are welcome to your Carters and Edelbrocks. They were a good platform in their day. I actually like the AFBs and AVSs. But again, there are simply better choices today. And have been for decades now.

Your turn...................................

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[rklein71]

One thing I am finding is the cost of AFB tuning parts. 15 bucks for jets, 13 for metering rods, 45 bucks for accelerator pump nozzles, fine tuning adds up.

 

[540HemiCuda]

some find it best to not feed the trolls
View attachment 146254

So much for civility.

Thank you for exiting. Juvenile name calling does nothing to support your position or advance the discussion.
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