[KEN CROCIE]

Here's my favorite 2x4 set up. Offy 2x4 with two 9776 Holleys. They are 450 cfm each for a total of 900cfm. They are flat bowl carbs which means they will mount inline rather than sideways. This simplifies installation with regards to fuel line and linkage. They are mechanical secondary carbs which means no vacuum secondary tuning.
A good alternative would be the AVB style carbs, Tom S can give you good advice on that style carb

[KEN CROCIE]

forgot to mention they were calibrated for open plenum intake (tunnel ram), and the Offy design would qualify as a low rise tunnel ram (open plenum)

[Skip Fix]

Some of the tunnel ram Holleys do not have power valves in them so if street strip I'd use a primary metering block with one.

[KEN CROCIE]

9776 Holleys are equipped with a -85 power valve. Kevin's Hallet flatbottom 425 Buick has a pair.

[Skip Fix]

I added them to a pair of 4224s and some 715 VS Tunnel ram carbs(what I ran on my 409 in '72) to use on a project. Hoping a bathtub will fit under a 65 GTO hood!

[Joog]

Originally Posted by KEN CROCIE

Here's my favorite 2x4 set up. Offy 2x4 with two 9776 Holleys. They are 450 cfm each for a total of 900cfm. They are flat bowl carbs which means they will mount inline rather than sideways. This simplifies installation with regards to fuel line and linkage. They are mechanical secondary carbs which means no vacuum secondary tuning.
A good alternative would be the AVB style carbs, Tom S can give you good advice on that style carb

Do you think that two 450s would be enough for my application? I see a lot of people doing dual 600s/650s/660s

[Joog]

Originally Posted by Skip Fix

I added them to a pair of 4224s and some 715 VS Tunnel ram carbs(what I ran on my 409 in '72) to use on a project. Hoping a bathtub will fit under a 65 GTO hood!

How are the 4224s on the street? Can you mount them inline?

[Skip Fix]

I have not run them but the 715s VS with the VS taken off sideways and all 8 bbls opening at once and no power valve was fine driving to high school and throwing my paper route!

[KEN CROCIE]

CARB SIZE. to determine if a specific CFM is required, the camshaft size must be factored in. What size cam are you going to use on your "street/strip engine. Let us know. My guess is that anything under 250 deg. intake @.050" lift, an 850 or two 450s will not cause a restriction to air flow.

[Joog]

Originally Posted by KEN CROCIE

CARB SIZE. to determine if a specific CFM is required, the camshaft size must be factored in. What size cam are you going to use on your "street/strip engine. Let us know. My guess is that anything under 250 deg. intake @.050" lift, an 850 or two 450s will not cause a restriction to air flow.

I asked my engine guy, he might get me a custom grind for what I need. Ill let you know soon

[tempest1964]

Offy 5499 with Carter AFB’s cloned like SD carbs. Stock dizzy set up by suntuned, here on the form.

[tom s]

Did John build those AFBs?Those are my go to carbs for non tunnel ram 2-4s.Tom

[tempest1964]

No, but he sure did help. First got inspired when I read his 2 part article on cloning SD carbs in Smoke Signals. Since I had never done a setup like this before, I reached out to John. Spoke to him several times for advice/questions. Still talk to him. He is a true gentleman and great guy.

[JLBIII]

Originally Posted by KEN CROCIE

CARB SIZE. to determine if a specific CFM is required, the camshaft size must be factored in. What size cam are you going to use on your "street/strip engine. Let us know. My guess is that anything under 250 deg. intake @.050" lift, an 850 or two 450s will not cause a restriction to air flow.

This is a timely discussion. My engine is out for a refresh right now. Currently running an 850 dp on a Northwind manifold but have always liked the idea of dual quad setup. Engine is a 461 with 10.8cr. KRE D-port heads that were just ported to 325cfm. Cam is 242/248 @ .050 with .585" lift. Car is used for street/strip running a 12 bolt with 3.91 gears and weighs 3470lbs without driver. Would the Tradewind intake with two 450's work for this combo?

[tom s]

pair of 750s on your 461.Run progressive and you will drive around town on the front 2 bbl of your rear carb.You will like it.Tom

[Joog]

Originally Posted by KEN CROCIE

CARB SIZE. to determine if a specific CFM is required, the camshaft size must be factored in. What size cam are you going to use on your "street/strip engine. Let us know. My guess is that anything under 250 deg. intake @.050" lift, an 850 or two 450s will not cause a restriction to air flow.

It'll be somewhere around this size

242/248, 540/563 with 1.5s

[tempest1964]

I would suggest you read this thread:
https://forums.maxperformanceinc.com...ight=Dual+quad
As stated in the thread multiple carbs are not cumulative. In other words, 2 450cfm carbs are not the same as 1 900cfm carb. Do your research before settling on carbs that are too small. Tom S and 61-63 are both very knowledgeable on this subject. 61-63 has built SD clones for years and knows them like nobody.
Good luck

[carbking]

Exact goal can also suggest carb size.

If you are looking at Carter AFB's

On your 461, best ET with a pair of the 750 Carters (4760s or 4762s).
Or maximum street drivability with a pair of 625 Carters ( 4759s).

You can make them look very close to SD carbs if desired.

Jon

[Skip Fix]

Just to throw this out as far as CFM sizes my 470" 409 we dynoed with two 750 Edelbrocks(I know guys!) vs 600 cfms. Same numbers so kept the 600s on it.