Hot Rods Dual quad setup on Chevy 283

Hi all,

I have a ‘57 Bel Air factory dual quad car (270hp solid lifter version), and am bringing it back from the dead. Because the existing induction was pieced together using incorrect WCFBs (a pair of identical ones from a ‘63 Vette) I’ve switched to a pair of Edelbrock AVS2 carbs, with a manual choke on the front and electric on the rear carb. I’m running the stock 3739653 intake with port-matched adapters to fit the Edelbrock carbs.

So, here is my question: I’ve decided to go with straight instead of progressive linkage after lots of research. I bought the carbs thinking I was going to use progressive linkage, and was planning to remove the choke assembly from the front carb. Now that I’m running straight linkage, is it ok to remove the choke from the front carb? If not, do I need to try return that one and buy another electric choke carb for the front?

Thanks in advance

 

I have two Carter AFBs on my big block Chrysler and after much research and speaking with John, @carbking, I run straight linkage and both have chokes, I linked the choke linkage together on the carbs and the manual choke cable is hooked to the rear carb and operates both. Works wonderfully and I haven’t even spent the time to really tune it

 

I run two Carter carbs with straight linkage and have both chokes wired open, I live in Buffalo NY and it only takes about 30 seconds of a slighty high idle before it idles on it's own.
You can see I just snipped the ends of choke cables with side cutters which crimped the inner wire in place to the outer jacket, then mounted it just like a standard cable.

 

I keep the progressive @ 90% efficiency which is high for your engine @7000 rpm would about 600 cfm you have around 1000 say 500 in the front half of the two carbs. If you open that much at 2000 rpm where the requirement is less than 200 cfm in a street car it will likely bog

 

Why the new AVS2s instead of rebuilding the WCFBs? While the WCFBs may not be 100% correct for your '57, the AVS2s are not even close if you are looking for a period feel.

 

Sold them to buy 20 Edelbrock's.

 

I like the 2 WCFB’s on my dual quads and would change them for any other carburetors. They are progressive, idle off both, and exhaust heat on the rear choke only. Front choke is not removed just adjusted to hold the butterfly open. They are set with a UniSyn which to me is very important. Both have the same brass tag number. Have fun with what you have.

 

Besides being incorrect, the WCFBs I had were missing a bunch of parts, and someone in the past had made a ham-fisted attempt at converting them for dual quad use. I don't want to fiddle with the car all the time, and am more interested in having something I can enjoy without having to think about it as much. I weighed the cost vs. convenience of rebuilt semi-original vs. new and no headaches, and I couldn't justify keeping the WCFBs.

My long-term plan, if it ever happens, is to put a modern chassis and 383 SBC under the car made to look like a '60s hot rod. When/if that happens, I'm going to keep and restore the original chassis and driveline to factory specs. I'll refinance my home at that point to buy a pair of correct 1957 dual quad WCFBs and a batwing.

 

Chokes removed from both carbs om my blown 392...

 

In talking to John he explained that dual carbs aren’t the same as just adding them up. I think he said about 70%. So that two 500s would be like one 700. I run mine straight linkage on a bone stock 383 and zero bogging anytime.

In terms of drivability you wouldn’t know the difference between them and the two barrel they replaced.


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Here’s my choke setup.




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I wonder how a 700 double pumper works on a 283 on the street with straight linkage that is what you have?

 

Well believe what you want, they work flawlessly on my car, your welcome to come try it out or just keep on insinuating I’m a liar... up to you


Plenty of factory stuff with straight linkage...

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That's not really an accurate analogy for how AFB carbs work.

 

If sunbeam would take the time to do a bit more research , he'd probably figure it out . the cubic inch /rpm / cfm formulas are fine for marketing but don't seem to jibe with real world experience. 2x450 holley / mechanical secondaries with 1:1 linkage for me , very responsive normal driving & 16.5 mpg for my 388 stroked SBC.

 

I am not calling anyone a liar but a 100 extra cubic inches that's 35% more will change things at the same rpm. As for the comparison to a double pumper you have 4 barrels with squirters opening together even if you dismiss the secondaries.

 

Well I think you will find plenty of people with dual 500cfm carbs on small blocks that are quite happy with how they work. Interesting that they only work on certain engines...


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If you're going to remove or defeat progressive linkage, then you'll want to keep chokes on both carbs. Normally the rear carb would be the primary carb, and it would be the only carb needing a choke. The secondary front carb wouldn't need to be choked as it would only be open at wider throttle opening.
I'd keep progressive linkage myself, as it just works better if set up properly, and carbs are in good shape.

 

56 was the eye opener for the hot rodding world at the time dual quads could be factory bought on just about everything and there were no “big” engines at the time. The dealer parts counter had them for vehicles that didn’t out of the factory with them.
Vic Edelbrock had them for the Ford Y-block in 54 for the 256 Merc and probably did the design work on the 56 Fords along with his own in 57. A relatively good tuner especially with a converted UniSyn can make them perform flawlessly even with a stock cam like the 225 and 245 Chevrolet’s and Corvette’s. The early carbs never had ratings but are thought to be in the 375 cfm rating and in pairs are a little lower. At a combo of 700cfm on a 265” would be a lot but still very drivable with the stock progressive linkage at the time. I believe the Cadillac’s linkage was straight and they like Chrysler’s had the bigger engines like Packards. Typically racers did not have those bigger engines in 55-6. 2 500cfm AFB’s were big as 400’s were on a lot of stock engines but with good driving skills and the weights right on the rear barrels hearing the sing with all 8 holes open is music to many of our ears.

 

I’m going to leave it at this, I am not an expert on dual quads but I did a lot of research, I highly recommend giving Jon @carbking a call, he is beyond knowledgeable and was very gracious answering my questions including some I didn’t know I had. Extremely nice gentleman.


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I read what your referring to that Carbking said. A factor over looked. How much cfm can a 283 pull? I'll leave it at that.

 

might be interesting to test a 283 on a dyno to test how much cfm...But so many have used the set up and it was a factory option, so maybe it's just fine...

 

[QUOTE="Johnny Gee, post: 14068839, member: 99339" How much cfm can a 283 pull? I'll leave it at that.[/QUOTE]
Don’t compare today with the 50-60’s that’s apples vs Orange’s. Today no one would use a 1.72 intake valve and cast iron heads or at least ones compared to back then. Same with the cam.

 

As far as I am aware, Carter published CFM figures for only ONE type WCFB. That was 2493s, used by Chevrolet on a special 283. This carb was rated at 380 CFM. This was a race-only carburetor for 1957.

The 2613/2614 and 2626/2627 were smaller, but the CFM was not published. At this time, the accepted "performance" measurement was venturii area, not CFM.

Carter DID "flow" the carburetors, but NOT for maximum air flow. Carter was interested in the A/F ratio at various values of vacuum. I have the flow-tests, but it is impossible to glean CFM from the tests.

The 283 original equipment dual quads were really too big FOR 1956/1957 TECHNOLOGY! And progressive linkage was used. Carter redesigned the 1956 carbs for 1957; did several service modifications (ones I remember were doubling the flange gaskets to increase plenum volume, and changing idle jets a couple of times); and finally redesigned the rear (primary) carbs for both the 245 and 270 setups in 1959. ALL OF THESE CHANGES WERE DONE BECAUSE OF DRIVEABILITY ISSUES! I can remember sitting behind some of the dual quad 'Vettes in the late 1950's at a stop sign (we didn't have many stoplights in podunk Missouri ). The idle would be very happy, and sound great to a teen-ager, and then the idle would get rougher and rougher, and soon the driver would blip the throttle to clean it out, and the black smoke would take care of any mosquito in a 500 foot radius

Driveability issues mean different conditions to different enthusiasts. What I am willing to accept today is much different than what I was willing to accept 50 years ago.

As to the argument of progressive versus straight linkage, a really good tuner can probably make either acceptable, at least to some enthusiasts. And again, we have better technology today than was available in 1956. Personally, ever AFTERMARKET dual quad I have ever sold, I have done with straight linkage. It sometimes is difficult on the smaller engines, but I generally use smaller carbs for street use than most would use. By doing so, I may leave 1 or 2 percent HP on the table at WOT, but trade that for superior driveability.

EDIT: Knowing the love some of you have for the Holley 4000, I almost hate to bring this up, but it has bearing on the discussion. Holley had the same problems as Carter with not having a sufficiently small carburetor for the dual quads on the 312. Holley's first answer was to machine rings which were added to the primary boosters to reduce the air flow:



This helped, but the carbs were still too big! So Holley restricted the opening of the secondaries. I discussed this modification at length with a NASCAR racer that won 3 Winston West championships. He laughed, and told me the first thing they did when they got the car was remove the secondary restrictions, AND WENT SLOWER! Putting the restrictions back made the car (and we are talking race now, not street) faster.

Jon.

 

Great stuff, thanks everyone! I think the path is this: keep the 1903/1904 AVS2 carbs (I’m past the return window, so that makes things a bit less complicated), add an electric choke to the front carb, go with straight linkage, then drive the car and see what happens. I know these carbs are quite a bit bigger than the WCFBs, but I’m hoping the newer technology will alleviate some of that. The adapters are effectively a 1/2” spacer, so maybe that extra plenum volume will help a bit.

I did forget to ask one thing on my OP; the carb pads on my intake manifold are the “figure 8” design that Chevy used, but the carb adapters are 4-hole. Think I should leave the adapters as-is or match them the figure 8 pattern on the manifold?

 

Your information is always welcome and enlightening. Maybe I was just lucky with my combination; an Edelbrock 257 on a 299” stock Y-Block with a matched pair of 1953 Oldsmobile small base WCFB’s. Seemed to be a perfect fit since Olds were 303”’s. Idle on both and progressive. With today’s fuel 12 mpg all in town about the same as a single 4 barrel. Can idle as long as I need or want with no smell or load up. Exhaust pipes are clean threw the bumper not like they were in the 50’s with leaded fuel. It’s a cruiser so opening them all up normally happens on the freeway early on Sundays with no hesitation up to a true 90 mph with more left.
I try to promote the use of dual quads because of their being traditional and have a special look but alway tell folks they do take maintenance. I’m lucky to be able to use mine year round.
Thanks again for all your information and help.

 

X2

I don't have the winter conditions you do, but mine work well in the coldest weather we have in central Missouri, as well as in the summer. So still can use them year round.

Jon.

 

I would use an open spacer so it better distributes an even signal from the engine, if you isolate each individual throttle bore of the carb to a specific runner on the intake it's going to be hard to have balanced cylinders.
As far as cfm on the afb style carbs, the weighted door on the secondary is pulled open by the vacuum signal from the engine, just because you have 1200 cfm the weighted door may be only opening up for 900 cfm of flow.
Speaking of 1200 cfm, this is it on a very mild 350, as you can see there is no issues at all.

 

This is not surprising.

For years, I assumed (wrongly) that the dual quad Corvette WCFBs were the smallest WCFBs that Carter made, because the primary side IS the smallest.

In more recent years, as I have digitized a lot of Carter and Stromberg data to where I can easily make comparisons and do research, I find that while the primary side of the Corvette dual WCFBs is smaller than the Oldsmobile, the secondary of the Oldsmobile is significantly smaller than that of the Corvette.

The result being that the Oldsmobile carb is approximately 7.5 percent smaller than either of the Corvette carbs.

So you are actually putting two smaller carbs on a larger engine than the Corvette. And the Oldsmobile carbs do NOT have the hokey diaphragm (ala Holley) that Ford used with the experimental dual quad WCFBs they tried in early 1956.

Would love to know the complete story as to why the WCFBs were not used for production, and why Ford ticked off Edelbrock by not using the manifold they asked Edelbrock to make for them for production. Based on Ford's history with Holley, I can make a guess; but won't.

Since you are happy with the result you currently have, you probably will not do this; but would be very interested in the change (if any) in driveability if you changed the linkage to solid.

Jon.