Carburetors for STR-12 Manifold

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DC 340 said:
Thanks all for your input. This is what I already did. : ) I ordered two Edelbrock VRS-4150 series #1307 rated 750 cfm. The 750 comes with annular boosters as the 650 does not. I think they will work for me.

VRS-4150 Carburetor 750 CFM #1307

Will post pics when they get here.
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Dual 750 carbs is a lot for the street, even on a stroked SBM. The Edelbrock AVS2 650CFM may be better. If you are used to tuning Holley carbs, they take a bit to get your head wrapped around. Once you have the calibration set they are like Rochester carbs, just drive it.
 
str12-340 said:
I've been running this on the street for 15 years now (340+.030). I'd be glad to correspond with you about an STR-12 on the street. It is set up with 2 500 Edelbrock performers (AFB), but I think if I were replacing them today I'd use 500cfm AVS2s. I'll send you a PM. My original lid was cracked and repaired twice but someone put me on to a fix that I can share that resulted in my never having the backfire issue. I can also send detailed pics of fuel lines and linkage. Right now my manifold is off (for the first time in 15 years) for pushrod replacement, so it's a good time to ask questions and request pictures as I reassemble it over the next week.


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Looks like a lot of carburation with stock exhaust manifolds. What goes in, must go out.
 
Anybody who already owns hipos will run them over the headaches of headers. Hipos look right at home in that beautiful engine bay.
 
Yeah, I've had this car since 1975 and have used about 4 different brands of headers on it over the years, but I wanted to drive the car and I really don't think this effects it much when it never really sees more than 5000 rpms. It has an excellent set of duals, and no flapper valve. The throttle response is excellent from 1500 to 5000 and I'm not hunting for a couple tenths that only a Chrondek would detect. For me headers are often just a headache and take away from my enjoyment of the car.

By the way whether you go with Edelbrocks or Holleys, I think it is important to use on demand secondaries. It's hard to "overcarburate" an engine when it only opens based on engine demand, as Chrysler figured out on six packs and their other carbs for cars that are primarily on the street.
 
BY the way the Edelbrock carbs that are tuned for dual quads are set up to be used progressively, which can be great for in line 2x4 manifolds, but are really inappropriate for an STR-12 where the right carb sits over the ports for the left cylinders and the left Carb feeds the right cylinders. A progressive set up would mean that one side was rich and the other side was lean with poor air fuel atomization a lot of the time. A look at the inside of the manifold makes that situation clear.

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When the need for more airflow presented itself Carter designed the AFB, Aluminium Four Barrel. The WCFB carbs were heavy with iron throttle plate, zinc float housing and aluminium cover. The AFB's used a counterweight on the secondarys air valve.
When they developed the AVS, Air Valve Secondary series they used a clock spring which is easily adjusted for tuning the air valve opening. The Thermoquad uses the same system.
This secondary air valve is opened by air flow through the secondaries so it automatically enriches the fuel when the mechanical secondary throttle valves open. The AFB counter weight can be ground to adjust opening while the AVS and Thermoquad are adjusted by tightening or loosening tension on the clock spring. This kind of functions like putting a different spring in the secondary vacuum pots to tune when they open.
 
str12-340 said:
BY the way the Edelbrock carbs that are tuned for dual quads are set up to be used progressively, which can be great for in line 2x4 manifolds, but are really inappropriate for an STR-12 where the right carb sits over the ports for the left cylinders and the left Carb feeds the right cylinders. A progressive set up would mean that one side was rich and the other side was lean with poor air fuel atomization a lot of the time. A look at the inside of the manifold makes that situation clear.

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Yes, you are correct on that point. That is why over carbureting the engine for street is a problem. You are better with carbs a bit small than a bit big. I would listen to the guys that say they have or are running the AVS2 500 carbs with good success.
 
Got the carburetors yesterday. They look good. Looks like I will need to use 1/2" carb spacers to enable the pass side carb throttle lever to clear the top. Fuel line and linkage challenges lie ahead.

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Both carburetors are mounted with 1/2" Moroso aluminum spacers. That throttle lever clears the top as I needed. The linkage at this point looks impossible to me. But I will get it I suppose.

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I don't remember what hood you will be using, but be careful. I could hardly get air cleaners to fit under the hood with my STR-12 with a stock hood (70 Dart) and NO spacers.

I took a bunch of photos as I put my linkages back in place a couple weeks ago and then I went away for Thanksgiving week. Did I ever send them to you, I can't remember...
 
str12-340 said:
I took a bunch of photos as I put my linkages back in place a couple weeks ago and then I went away for Thanksgiving week. Did I ever send them to you, I can't remember...
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You never sent them to me. If you have time, I would be very interested in seeing them. I am in the middle of trying to engineer my own linkage. Not fun. : ) Thank you!
 
Trying to get linkage pivot enough aft of pass side carb allowing me to at least connect the 2 carbs with Enderle stuff. This should work.

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seems the whole shaft is way too close to the firewall for good solutions
 
Both carbs are connected. I am planning to swoop in with a longer throttle cable if I can find it, mount throttle cable bracket to driver side rear carb stud if possible. Throttle cable would be independent of carb connections.

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DC 340 said:
Both carbs are connected. I am planning to swoop in with a longer throttle cable if I can find it, mount throttle cable bracket to driver side rear carb stud if possible. Throttle cable would be independent of carb connections.

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True, the th
DC 340 said:
Both carbs are connected. I am planning to swoop in with a longer throttle cable if I can find it, mount throttle cable bracket to driver side rear carb stud if possible. Throttle cable would be independent of carb connections.

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True, the throttle cable will work best or easiest for the first carb, which in turn would operate the second one, with its mechanical linkage. I would think you would need a Heavy Duty cable. Dodge vans used solid rods for their carbs, pedal to carb (early to mid 70's). Their kick-downs were also solid. When I installed the 340, I had to do a little adjustment to connect the AVS, but kept the solid linkage. It worked great.
 
Here's the Bouchillon throttle cable bracket I modified to fit. Bought longer new Pioneer throttle cable I believe will work. Still a work in progress.

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My final throttle cable attachment for now. :)

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My 1st attempt at using the rear vacuum port as a pressure relief in case of backfire. An NPT fitting with barb outlet. Neoprene rubber cap with a tight fit.

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