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dual quad setup

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Old 08-27-2008, 12:01 PM   #1
mlager8
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Default dual quad setup

Going to be doing a dual carb setup and was just asking advice from anyone who's been there on things to look out for, what to do and what not to do. Is there a reason why all pre built dual carb and intake set ups use 2 edelbrock avs thunder series carbs instead of 2 1405 500cfm carbs? Will 1405 not fit a dual quad intake? Just asking becasue the 1405's are $100-$150 cheaper than the avs thunder ones. Also if I use an intake other than edelbrock will I have fitment issues with edelbrock carbs?
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Old 08-27-2008, 02:11 PM   #2
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What size engine? I used dual Holley 4160 465cfm carbs on my .030 over 289 years ago. I had a Ford intake that mounted them backwards like a 427. I would think the 500cfm carbs should work, as far as I know thw AVS and AFB share the lower casting physical size. Just remember that the rear carb in this setup is the primary. Back when Carter made them they had some carbs designed for dual setups where one was complete and the other lacked a choke and fast idle linkage.
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Old 08-27-2008, 03:19 PM   #3
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The engine is a 289 also .030 over, I'm aware the secondary carb dosent need a choke, but it seems that the dual carb and intake packages today come with one manual choke and one electric choke, not sure about the fast idle link but I'll have to check in to it, thanks alot lebaron
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Old 08-27-2008, 05:53 PM   #4
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i'm running the F-28 from edelbrock with 2 500's both with manual choke. have had no trouble with them and love the way it runs and still gets around 15 to 16 mpg down the highway with a 5speed not the cleanest of motor bays but its getting there
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Old 08-27-2008, 09:03 PM   #5
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just realize, running dual quads on just about any engine is mostly for show and not go, they make alot of sucking noise and look cool but I can put money that you will never find a dyno test that shows dual quads making more hp anywhere compared to a good single quad setup. The exception would be a pretty radical motor with a tunnel ram.

Too bad they dont make a dual plane tunnel ram, even the new edelbrock rpm airgap dual quad setup doesent make as much power as their rpm air gap single carb.

Sad but true...........
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Old 08-28-2008, 12:19 AM   #6
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Thanks for the input, is there really no gain from running dual quads? The reason I want to run a setup like this is really because I'm doing a Shelby clone, GT350's came with a hipo 289 and dual quads and I want everything to at least appear close to stock. I'd love a GT500 but a 428cj and police interceptor t6 is just way out of realm in terms of budget.
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Old 08-28-2008, 08:42 AM   #7
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Prostock drag cars use tunnel ram "sheet metal" intakes with dual quads. They also run a big scoop on the hood to feed them and need the added air flow due to having over 100%VE and huge displacement. In a street motor with a dual plane intake, I agree with htwheelz that you will have better performance with a single carb. A 289 only needs 550-600cfm of air/fuel. Why would you ever need dual 500s? WAY overkill. Even bigblocks that require 1000cfm are better off with a dominator than dual quads. You really need to be up there in volumetric efficiency and cubic inch displacement to need the air flow dual quads give. In muscle cars, multi carbs are all for show, will probably hurt your performance, and are exponentially harder to tune. In the old days they thought more carbs were better (i.e. the dual quad and the six pack), but since computers and performance testing have evolved, we now know a good single carb is a better way to go. Same goes for intake runners on heads. They used to think bigger way better, but we now know that there is a sweet spot to carb and runner size. Edelbrock does not even give a power range rating for their dual quad intake. If you call them up, I bet they tell you to use an Air Gap single carb setup for performance. If you want it for looks get after it, but be prepared to spend a bunch of time tuning. You can always run an oval air cleaner with a single carb to give the dual carb look...
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Old 08-28-2008, 09:53 AM   #8
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Thanks urban, didnt realize a dual quad setup would take away so much from performance, At least I thought little or no gain, but never thought it would take away. Just for the sake of looks would dual holly 350 2 barrels give the same performance as a 600-700 4v with the added look or would that still detract power?
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Old 08-28-2008, 02:13 PM   #9
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The dual quads look really neat. If you choose to go this way you might want to check out www.pricemotorsport.com for an intake and carb set up. They will sell both Holley or Edlerbrock. I think these manifolds are closer to stock looking than the air-gaps. Just a suggestion.

Oops. I just realized that they only show a 351W manifold and not a 289/302. You might call then just the same.

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Old 08-28-2008, 02:56 PM   #10
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I am not sure how two carbs compare to a single carb with respect to air flow. Do dual350s equal one 700cfm? I do not know the answer to that. I would guess yes. As for dual two barrels versus a single four barrel, I would guess you are better off with a single four barrel vacuum secondary due to the secondaries coming in when you need them instead of two two barrels pouring fuel all the time. That dual setup would be like a four barrel with four primaries...a gas hog! I think the issue with dual carbs is the intake setup. The dual plane design for dual carbs is just not as good as a single carb intake. There is a big difference between dual plane intakes and sheet metal tunnel rams! I am suggesting from what I have read that you need a tunnel ram type intake to allow the dual carbs to work correctly. If you do not have that, then you will have better performance with a single carb. If you want to cut a big hole in your hood, mount a bird catcher scoop, and move your power band way up with a radical cam, you could probably take advantage of dual carbs. I preface all of this with this is my opinion based on articles I have read about dual carbs and the trend away from the multi-carb intake in the last 40 years.

Here is a article and test run on a 400cid chevy small block with dual quads vs single quad. Spoiler...the single carb wins.
http://www.superchevy.com/technical/...est/index.html
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Old 08-28-2008, 03:09 PM   #11
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I've heard good things about the Pony Carbs 3x2 setup. While it's still probably not as efficient as a single 4 barrel setup, it certainly has the wow factor
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Old 08-28-2008, 06:28 PM   #12
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I see your point urban, I'm def not going the tunnel ram route, the whole point of the dual carb setup was to appear close to a stock GT350 289. Like you said, an oval air cleaner would hide it well but I guess it's just not worth the power loss to go dual quad. too bad it would look damn sweet Thanks for the article and advice
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Old 08-29-2008, 08:47 AM   #13
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mlager8 its your car build it the way YOU want it.i personly love my motor setup with dual
quads like i posted before i'm running two 500s the most tuning i've had to do was lean the idle screws.it runs and drives great. and even with 2 motors built just alike on a dyno they will not make even HP#s they even said in the article they should have swaped intakes. articles are good starting points but as joe sherman told me and a buddy of mine when he was doing a set of heads for buddys car. about the articles they did on him DONT beleave everything you read. if 2 4s are the look you want dont worry about 0 to 40 HP unless you going to be doing alot of racing.with 2 500s they to are vac secondaries.and as htwheelz67 said they dont make alot of sucking noise all i hear is my tires and the motor hitting 6000 and it sounds really good doing it
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Old 08-29-2008, 12:02 PM   #14
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A 2x4 intake would work fine and make good power. Use a progressive linkage so you'll only run on one carb till you get on it. A dual holley intake would be cool, but they're hard to find. I have an old weiand 2x4 intake for carter/edelbrock carbs sitting in the garage. :-)
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Old 08-29-2008, 12:02 PM   #15
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Quesey, with dual 500s on a 289, do your carbs even open the vac secondaries? Do you have both carbs' primaries opening at the same time? That seams like WAY too much carburetion for a small block of anysize. I do not see how both quads are really opening all four venturies. Maybe your vac secondaries are not opening which would explain why you have not had to tune much. If you had two mech secondary quads, you would run WAY rich at WOT...I would think.

Gary H, I agree a dual carb with progressive linkage would be cool, but again I argue to do it for the cool factor and not the performance b/c a single carb would work better.

mlager...do what ever you heart desires. I do not want to influence you to do something you don't want to do. It is your car, I just post here to help guys not bang their head against the wall if they do not plan to...:-).
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Old 08-29-2008, 12:16 PM   #16
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Quote:
Originally Posted by urban_cowboy View Post
Here is a article and test run on a 400cid chevy small block with dual quads vs single quad. Spoiler...the single carb wins.
http://www.superchevy.com/technical/...est/index.html
they shoulda used a big block...



2x4 FTW!

love ours. and its a hell of a lot easier to tune then they were back in the day
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Old 08-29-2008, 01:07 PM   #17
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I could see using 2x4 on a 500+cid bigblock for streetability. It is not easy to get vacuum secondaries and electric choke on a 850+cfm carb.
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Old 08-29-2008, 04:17 PM   #18
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I may be wrong... but I though the Shelby 289s just had the one 670 CFM holley on them??? Dual quads? Are you sure?
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Old 08-29-2008, 04:57 PM   #19
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Quesey, with dual 500s on a 289, do your carbs even open the vac secondaries? Do you have both carbs' primaries opening at the same time? That seams like WAY too much carburetion for a small block of anysize. I do not see how both quads are really opening all four venturies. Maybe your vac secondaries are not opening which would explain why you have not had to tune much. If you had two mech secondary quads, you would run WAY rich at WOT...I would think


mine is a stock short block from a 91 mustang (302) and yes the secondaries do work and open.

yes both carbs are tied togethet both open at the same time.

now is it to much would it make 20 or 30 more HP with 1 carb maybe but as i said to mlager8 if he wants 2 4s then do it as i told people when i built my car when they pay for it they can use what they want. the 500s you buy as a kit from edlerbrock with intake are set up for dual 4s dont know what they do diff there website will tell you theres 500s for dual 4s

AND people love the way it looks and so do I ...............
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Old 08-30-2008, 11:21 AM   #20
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Thanks to everyone who replied, still love the look of the dual quads. Gunna ask around at the carshow this weekend, if the power loss is negligible I'll probably do the dual quads as originally intended. I guess ur right quesey, I'm not doing insane runs at the strip every weekend so the difference in hp is probably not even noticeable on street.
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Old 08-30-2008, 11:21 AM
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