Dual quad need less cfm

[Footjoy]

I want to put 2 fours on small block for wow factor only have about 300 horsepower. My question is can an edelbrock 500 cfm carb be modified to 350 400 cfm? I only need about 600 cfm but want the look of 2 fours.

Thanks

[CSI:QUINCY]

I don't know of any way to make a carb smaller but you can adjust the linkage to make it so the front carb barley operates at full trodal so that you are not over carbing the engine.

[Footjoy]

Is it the front carb or back that should not open all the way?

[andrewb70]

I don't mean to be rude, but the only "WOW" factor your going to have is; "WOW" this runs like crap...

Andrew

[BlackGMC]

Maybe you could go with 2 X 2barrels?

[HILROD]

I have installed a stock early sixties type dual quad set up on a bone stock 80's chevy pickup. It ran great! The carb sizes might be just slightly smaller that a 500 cfm. Of that I'm not sure. As long as the manifold is a low rise type, and it is tuned right, you'll have no trouble. With most progressive linkages the rear carb opens first and just before W.O.T., the front opens. Basically two barrels at a time. Also if need be, the front carb could have the secondarys disabled. That probably would not be needed. FRANK

[Footjoy]

Thanks Frank, I cannot run with the big dogs and throw 5 grand at this on LS I appreciate your answer I would like to put tuneport on but I am not technilogically up on this stuff.

[Skip Fix]

The smaller AFB type Carters or Edelbrock clone versions can be made to work decent on a dual quad setup for the street as they have a vacuum secondary. But they are harder to tweak the secondary opening than a Holley.

There are also some small Holleys,I think even 450 cfm. shoot some of the circle track classes used a 390 cfm double pumper.

Using a progressive linkage as described has you run off one main carb then at WOT the other comes in. This is how many of the old factory dual quads and tri powers were. Often only the main carb even had an idle circuit.

Being an "old guy" I drove a dual quad car on the street for several years, lots of folks drove tripowers also. They can be a little tempermental to get dialed in but can work fine on warmed over motors, the factories did it for years.

[LS6 Tommy]

If you can fit them on the manifold, Holley vac sec carbs would be ideal. Any vac sec will be a better deal than a double pumper as they're never oversized.

Tommy

[fast Ed]

Would the "Thunder series" AVS style carbs from Edelbrock, the ones with the air flap on top of the secondaries, work any better for an application like this? They do have that type in 500 cfm.

http://www.edelbrock.com/automotive_.../thunder.shtml


Depending on tranny, axle ratio, etc., you may be able to get away with that.

On the 289 in my Cougar, several years back before we started modding it heavily, the intake gasket was leaking, and the original 2V carb was bunged too. So since it all had to come off, I wanted to put something more interesting on for a while. I borrowed an old Offy low-rise 2 x 4V intake from a buddy, that had two Carter AFB 500 carbs on it. Stock engine, C4 trans, 3.00 gears, it was pretty doggy up until around 80 mph, but I expected that.

Much better with the EFI on it now, but the 2 carbs with little chrome air cleaners, which just fit under the stock hood, did look pretty cool.


cheers
Ed N.

[rockvillespeed]

the carbs dont have to "made smaller" - they're load-sensing secondaries that're only gonna open far as the engine needs them too, so if you have the carbs already, bolt on and start tuning.
holley makes a 450 cfm carb meant for dual quad use, and they are very inexpensive new; and the tune is pretty close for a mild motor out of the box.

[chicane67]

Why not run dual 390 cfm, four barrel carbs ??

[fast Ed]

Depends on the style of intake ... some of the ones for small block engines do not have enough room between the carb pads for clearance on the float bowls of Holleys mounted end-to-end. Hence the popularity of Carter AFB style carbs in those applications.

An alternative is to use adapters to run the Holleys sideways, but that makes the linkages more complicated obviously.


cheers
Ed N.

[MonzaRacer]

Well actually I would have to look for the numbers but Holley made a 465 Holley that was better for dual quad use as it was a smaller "mimic " or clone of the 1850 Holley 600cfm.
The 450's have carb specific parts from what we found way back when.
I had a 225 slant six bored .185 over and stroked 1/2 in and ran 2 465 cfm holleys and it ran great. Now I never ran one or the other I just linked them ,then hooked up the throttle and the performance was awesome.
My personal preference would be to make sure you have a good ,mild mid range cam and not some lopeyrace cam.
As for running on one I dont like it as it give real wierd fuel ditribution.
As for the Thunder seires they tune pretty much like a Qjet secondary. Where the performer (AFB) has a weighted air door. Dont get me wrong I love AFBs I have one in my living room on bench and I am trying to trear it down asthe shafts are stuck.
The big issue with multiple carbs are the tune. Get a wide band O2 for each bank and tune for good cruise then tune for WOT.
Another thing is dont be stingy with timing. I have found that a lot of people wonder about mileage but they have been real stingy with timing and timing curves.
Another thing to remember is let one idle screw set the base then tune the pairing. I like to find a way to set a unisync up on duals to get the air flow right. I have found that the best set up is to get matched carbs from say The Carb Shop in California. Before he died Brad Urban ran that and set up my holleys for me and it was awesome to be able to final tune it.
Another possibilites would be to think about dual throttle body FI. I remember they did an article in one of the magazines on it.
I would step up to a RacePumps mechanical pump and take a look at Megasquirt. Set it up with no ignition control just make it a closed loop fuel system and tune the timing manually.
The O2 would run the guel mixture after you get it uned in and the mileage would be incredible for a dual set up. and with proper air cleaner you would never see the injectors and having good cold start characteristics is good.
I really dont see it cositng anymore than dual carbs. I would thing say 2 throttle bodies from a 2.8 S10 would be right on track and if they dont flow good enough ,step up to 4.3 TBIs. and you can get them from the salvage yard.
And if you want to later on the Megasquirt can be set up to run TPI.
Me I found an old Hilborn mechanical EFI and wanted to try to make it rune with Megasquirt but the owner wouldnt sell it so I am still looking.
The neat thing about MS is that it will run mild to wild and even boosted systems. You cna buy the box ready built and then you use a cheap laptop to tune it OR they have a setup called MegaView that lets you do some tuning and monitor all features of the software.
My buddy went on Ebay and bought a simple AMD powered laptop with an old K6-2 550MHZ processor to tune his and just leaves it in the car as if someone steals it they got nothing.
We were using an old lap top with an old 486 processor , very slow but it ran windows 95 (to tuning software like win98 better).
And this box if it has some type of electronic problem it cna be fixed pretty easy and the internals (with the exception of the processor and map sensor) only cost about $85 .
For what it costs and its adaptability its pretty cool.
Also on a different note the dual intake could be set up with 2 matched 2 barrels and with proper air cleaner most would have to look twice to catch it. I have seen several show cars like that.
Good Luck
Lee

[rockvillespeed]

hi skip,
we gotta stop bumping into each other like this!
(speedshop)mike

[Footjoy]

Dual tbi didn't corvette come out with that arrangemnet in the 80's, called crossfire injection.

[slowcamaro]

Dual tbi didn't corvette come out with that arrangemnet in the 80's, called crossfire injection.

Didnt it suck?