The advantage of dual quads is only seen in all out racing. In maximum effort you want the cylinders tuned evenly, jetted for the same AFR all the way around so there's even fuel delivery to all the cylinders. That's why tunnel rams and dual quads are prefered for maximum effort FULL RACE drag engines. 1 barrel for each cylinder, it lets you tune each cylinder individually by changing the tuning on each individual barrel. That being said, they're primarily used on Pro Stock engines that are 500cid and around 130%+ volumetric efficiency and operating between 10,200 and 11,000rpm. The pinnacle of naturally aspirated powerplant design, putting out over 1,300hp all engine on gasoline.

They have no place whatsoever on any street car and about 90% of race cars, other than for looks. You can get them to work, and they're a pain to tune, but they'll always make worse mileage and worse power. That's more a factor of carb size. If someone made 250-300cfm carbs with a modern 2x4 then it could be a sweet setup. You could use a set of 390's from Holley, but no one makes a modern 2x4 intake with good flow balance. The modern single 4bbl dual planes have better flow balance characteristics, and a tunnel ram is basically useless under 7,000rpm.

If you want to go that route, you could go to a Webber setup using something like DC0E's in a 4x2 configuration. 4 2bbl Webbers in a downdraught setup, but it's easily as expensive as a badass EFI setup would cost and you have to know how to really tune carbs, and how to really tune Webbers in particular. And there's just not much support for Webbers here in the US.

If you're intent on going with a 2x4 setup, then stick with a set of 390's from Holley. No one will really know the difference on the outside, and it'll run really well.

And I take it back, Edelbrock apparently now makes an RPM Air Gap dual quad. You could try that with 2 390's.

 

I'm almost thinking a std dual quad intake with 2 350 cfm or autolite 2bbls adapted to it may run better than 2 4bbls.

 

Or a good 4bbl with a nice dual plane intake.

 

I tried to post a reply to urban cowboy the other day, but I got kicked out while typing it. I ran 2 465cfm Holley model 4160s on a Ford individual runner manifold originally designed for the 66 Trans-Am Mustangs. I don't remember the PN on that. I had the carbs mounted backwards like the 427 and used the 427 style secondary diaphram setup with the synchronising hose. The carbs were progressive, front primaries opening first, followed by rear primaries. Only the front carb had a choke. Both secondaries would open together giving a total of 930cfm. Yes, according to all the formulas it was too much. Tell that to the Corvettes, Trans-Ams, Challengers, GT500s etc. that I outran with the car. It was a 1966 GT350, 3.89 Detroit locker, F70-14 tires and a wide ratio T10. Oh, it got 18-20mpg at the then 55mph speed limit, 22 if I ran 75-80 with it. This before Duraspark ignition, just plain old Ford Hi-Po 289 dual point. As for 3 2bbls, I had Ford kit C4OZ-6BO68-B I think it was on a 1964 Falcon with a midly modified 260. It did vey well even with a C4 once I figured out the tuning on them.

 

My 1965 289cid has two 390 cfm holleys.
Originally it had one 480 cfm holley.
Cam is Comp cam, FS Nostalgia 271S+
Solid lifters.
Runs very well.
No flooding or hesitation.

 

Many cars, in the 50's and early 60's had them. The Plymouth Fury, for example, depicted in Christine did, and that was a family car. Thousands of 56-61 Corvettes had dual-quads, and of course the 67 GT500 had them. A dual-quad intake was planned for the 67 GT350, but it was cancelled. You could buy it over the counter, of course, it was already available as an add-on.

 

HELLO;

A GT350 never came with dual quads, it had an aluminum high rise with a 715 cfm "lemans" style holley carb with mechanical choke and vacuum secondaries.


.

 

No prob, just limit the secondaries so the only open around 1/4" of the way and use progressive linkage between the two carbs so just 2 barrels on one carb open first as one suggested.

an oval air cleaner will not hide dual quads one iota.

.

 

the loss comes from opening 8 barrels on 2 4 barrel carbs too soon.

 

yes it would and it would still have the wow factor as in "wow...why the heck did you do that, it looks silly?"