dual 4 barrels

Got a question for all you who have run dual quads on a SBC. I have a 305 bored to 315 with a small cam 218/224 dur. @.050 and I'm running a 600 cfm edelbrock carb with a dual plane intake manifold. I have 1-5/8 headers with a MSD coil and Distributor. Rear is a 9" ford with 2:76 gears. I traded a used 3 deuce set up for a polished edelbrock intake with dual 500 edelbrock carbs. I would like to run this on my engine using only one carb but have it set up for progressive linkeage where I would have the second carb only open it's secondary's part way. I love the killer looks of a multi carb set up and it's not just for show as I put on about 2500 miles in the summer. Would this combo work or am I asking for problems?

It would seem like 390CFM carbs would do better but as long as you put enough slack in the second carbs progressive linkage, seems like it should work ok.

Go for it. Dual-quads are my favorite. I doubt that you'll ever get into the secondaries of either carb, the primaries of each carb should fulfill the needs of the motor at WOT. I'd run the rear carb as the primary carb and set up a sliding rod arrangement to pull the primaries of the front cab in at about 75%, so that the throttle blades of both arrive at WOT at the same time.

There's nothing quite like the sound of 2-4's suckin' for all they're worth :)

i have a offy 2x4 intake edelbrock,carbs, you might be overfueling a bit, on a 305,but jet it down a bit, should be o.k
i set it up to run off the front choke, complete with an electric choke,back carb starts opening up at about 2800 rp's

yes they look good .the thing that i can think of is that the idle may be a bit hi but could be tune in. that is the one thing that may give you some troube the more cfm on the small engine may be hard to turn down them all the way down but can be work out go for it

Carbs are a little big for the engine a cam you're running, but it'll work if you jet the primary carb back. If it were me, I'd run the back carb as the primary, gut the front carb and run a slider type linkage from the rear to the front so that you can determine when and if you want the front carb to come in. I ran a setup like that on the sbc I had in a '36 coupe.

I agree Tech, you will probably do fine with the set up. He and NTFDAY also right about the linkage set up.

Set the rear carb up as the primary with the functional choke, and either disable the front carbs choke or remove it.

Thanks for the info Thats how I was going to run it with the slider type linkeage. Both carbs now have electic chokes and I will pull one off. Might lose some of my HP and torque but what the hell. It will still run good and the sound like tech says of both openiing up will justify the change over:D

What about running a stromberg 97 EFI setup, where the carbs are gutted and have the injectors inside, you would have the look, with the reliability of EFI

Matt I was lookiing into that but I got the better part of a deal with these dual 4 barrels, so I'll give them a try.

I run a couple of Carter 500 cfm's on a 462" Buick.
Granted, a bigger engine than your Chevy, but it's a nice setup.

Straight linkage is used and secondaries are not a problem with the big engine nor will they be with your smaller engine.

Carter/Edelbrocks air valve open to what is required for the engine.
Which is to say, do not adjust the carbs - or secondary carb if progressive linkage is used - to limit the secondary throttle opening.
If you do, you'll also limit the primary opening due to the primary and secondary throttle blades operate in unison and rely on the air valve opening for proper airflow.

I don't see anything wrong with using progressive linkage as long as you build a good one or buy a good one.
Edelbrock - I believe - has a good one.

Some of the cheaper progressives, especially those on triple 2 bbl setups leave a lot to be desired and some of them in fact are dangerous to my eyes.

With the big Buick running a 284-292 adv. duration cam and the straight linkage dual quads it will idle at 600 rpm all day long.
Throttle response is excellent as well.

You'll have to pay a little more attention to the setup when using dual quads on a smaller engine, but it's not the black art that some make it out to be.

I bet those dual quads looked real nice on that big buick engine. What did you have it in?

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Originally posted by chevy 37
I bet those dual quads looked real nice on that big buick engine. What did you have it in?

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32 Roadster.

Here tis, home-made fuel log, home-made air cleaners, home-made linkage etc.

Now running a 750 Carter on an Edelbrock Performer with a milder cam.

The carburetion and big cam are going into the car on the next post.

A slightly different view of the fuel block and linkage.

Counting fittings, aluminum stock, Heims, stainless rod, perhaps $50. invested in everything.

And here's a pic of the new project . . . 31 A roadster on 32 frame rails.

Also a 455 Buick which will end up 462" and right around 540 # torque.

At 2200# total vehicle weight, should be fun....

Fwiw, here's the 32.

I guess it will be fun. Alot of torque and HP in a light car. Ever your down my way, would love a ride in your roadster. I made my own fuel log that looks similar to yours. As soon as the weather warm up, I'll be taking my old intake and carb off and putting on the dual 4r's. You got some great looking vehicles.

Auburn, California?

I moved to N/W Arizona summer before last.
Came from Visalia, California and know quite a few hot rod types there.

About ten years back I sold a project 39 Ford four door to an Auberry, California auto parts owner.
Auberry is near the Edison Big Creek hydro generation project.
Always wondered if he ever got it running, just about all the specialty parts for an SBC, T-350 9" car with solid axle were there.

I'm not sure where Auburn is.

Unfortunely Auburn is in the other direction like NYS. My wife and I are moving to Wyoming sometime in the future and then we could make it a shorter trip.

Not to hijack Chevy37's post here, but the subject has tweaked my memories in these last few posts.

Hey C9x, you're talkin' about my past, here. I was employed by SCE for over 35 years and worked all over the service territory, and when I retired, we moved to a mountainside some 15 miles northeast from Auburn - sort of between Auburn, Grass Valley, and Colfax. The cold winters finally caused too much concern for my physical well being (wrecked ankles and icy ice don't get along too well), and we sought out warmer climes - we sure did get "warmer", in spades with the move to Las Vegas, although, the other morning it was 28 degrees when I got up at 0600. Whereabouts in N/W AZ are you?


By the way, Chevy37, I, too, think you're on the right track - some good advice here, as always seems to be the case; dual quads have their own special appeal.

Thanks Rrumbler. 28 in Vegas. Damn that's colder than upstate NY

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Originally posted by Rrumbler
Not to hijack Chevy37's post here, but the subject has tweaked my memories in these last few posts.

Hey C9x, you're talkin' about my past, here. I was employed by SCE for over 35 years and worked all over the service territory, and when I retired, we moved to a mountainside some 15 miles northeast from Auburn - sort of between Auburn, Grass Valley, and Colfax. The cold winters finally caused too much concern for my physical well being (wrecked ankles and icy ice don't get along too well), and we sought out warmer climes - we sure did get "warmer", in spades with the move to Las Vegas, although, the other morning it was 28 degrees when I got up at 0600. Whereabouts in N/W AZ are you?

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34 years as an operator at:
Saugus Sub,
Colton Sub,
Saugus Sub,
Pardee Sub,
Rector Sub.

Kingman, Arizona.
3300' altitude, temps are usually 10-15 degrees less than at Laughlin on the river and about the same as compared to Las Vegas.

14 degrees here at dawn last Friday . . . and 26 degrees inside the garage.

I gots wrecked ankles as well, but not too bad.
I just get reminded of all those trips over the handlebars of a dirt bike when the weather is cold.

My daughter lives in North Las Vegas and we go there now and then and go to Laughlin fairly often.
Cheap entertainment at either place if'n you don't gamble.

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Originally posted by chevy 37
Unfortunely Auburn is in the other direction like NYS. My wife and I are moving to Wyoming sometime in the future and then we could make it a shorter trip.

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My granddaughter lives in Wyoming, close to Casper.
1 degree above a few days back.

She's learning that Kingman weather was nothing compared to the weather they have there....

Yea the weather can be bad in Wyoming, but were thinking of moving to Cody were it's not as cold and their total snowfall is less than 20". We were out there this October and it was in the 80's

TO un-hijack the thread for a moment ;) I'd recommend the Holley 4160-series 390 cfm carbs, P/N 8007. I run two of them with a straight linkage and stock jetting on a 5.0L H.O. and it runs killer. Good luck, man -- two fours is a beautiful thing! If you run the dual 500's, keep us updated.

Ever had any trouble synchronizing your holly 390's. I heard they were a pain in the ass to calibrate.

So . . . just what does happen if the carbs aren't perfectly synchronized?

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Originally posted by chevy 37
Ever had any trouble synchronizing your holly 390's. I heard they were a pain in the ass to calibrate.

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Not that I'm aware of. I rebuilt them completely before I put them in; that might have helped. But they haven't given me any trouble and all I've done to "tune" them is adjust the slider on my homemade linkage and tweak the chokes a bit.

The linkage:

http://memimage.cardomain.net/member...178_9_full.jpg

They ran fine until this new build, when I had all kinds of vacuum leak problems; I ended up replacing the #!%%&ing power valves a few times while I was chasing the leak. I'm going to tear them down again this winter and put the blowout protection thingies in. Stupid Holleys. :cry:

I think that tuning / balancing dual carbs may be more of an issue when you're egregiously overcarbed; I was told numerous times that I had to be meticulous about tuning them but they literally swapped right in on both the old 302 and the new 5.0, tunnel ram and all -- turned the key and it ran killer. Minus the vacuum leaks, mind you. :rolleyes:

I know one other person who ran dual 390's and he had the same experience. Dual 390's are obviously smaller than the 850 Street Compensator or whatever monster quad is the rage these days. I know a guy who told me to scrap the idea of running a dual-quad tunnel ram because he once had dual 750's on a SBC and, I quote, "It was impossible to tune. It never ran right."

I'm glad you didn't really have any problems with yout Holly's. I've never run dual quads, but quite a few tri carb set up's and all were hard to get them properly tuned. I'm going to make my own slider system where I'll use just my front 4 barrel and when I want WOT I'll have the second carb cut in only part way. Hopefully that should work out OK.

Quote:

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Originally posted by chevy 37
I'm glad you didn't really have any problems with yout Holly's. I've never run dual quads, but quite a few tri carb set up's and all were hard to get them properly tuned. I'm going to make my own slider system where I'll use just my front 4 barrel and when I want WOT I'll have the second carb cut in only part way. Hopefully that should work out OK.

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I suggest that fuel distribution will be a little better if you use the rear carb as the primary and pull the front carb in later.

Here's a Q that my antique mind has been pondering: If you use the rear carb as the "primary carb", wouldn't the fuel distribution from the primaries in it be more equal than if the front carb was used as "primary", since the front carbs primaries are all the way to the front of the manifold, as opposed to the rear ones being more to the middle?? This all being as if you used only one carb for a single pair of barrels at lower engine speeds; if both carbs are used in tandem, with the secondaries coming in at some predetermined point, then this question is probably moot.

Ooops! Tech, you beat me to it, by just one minute.:LOL:

One set of primaries on a single 390 doesn't seem to keep the engine afloat; at least, not with the tunnel ram. It idles for about ten seconds and then sputters and dies. I tried running it on one 390 when I needed parts for the other; figured I'd just block off one hole and the related vacuum / fuel lines and run to Schmuck's on one carb, right? Not.

I planned on someday trying to run the carbs progressively until I tried to run on just one.

Richard, Rumbler your both right, never gave it a thought. Thats why I ask questions because sometimes this old mind of mine doesn't think right. Thanks for your input.

The more I got thinking about what you said, I have another question for you. If the front carb was used for your primary, wouldn't under acceleration all gas would move to the back carb, and if your rear carb was your primary one wouldn't the gas puddle in the back of engine and cause the front cylinders to starve for gas? Just my thought.

I don't think the horizontal G-forces on such a lightweight thing as a fuel/air mix would affect it more than a negative pressure which will pull the air/fuel mix into the cylinders.

The rear carb is chosen since it's primaries are closest to the center.

I found on my 462" Buick the dual quads ran a bit rich at the front end.

Straight linkage fwiw.

Quote:

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Originally posted by chevy 37
The more I got thinking about what you said, I have another question for you. If the front carb was used for your primary, wouldn't under acceleration all gas would move to the back carb, and if your rear carb was your primary one wouldn't the gas puddle in the back of engine and cause the front cylinders to starve for gas? Just my thought.

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If that were the case, I think all the manufacturers would have mounted the carb at the front of the intake instead of in the middle, wadda ya think??

I think that there is not enough TIME for the mixture to move anywhere except from the carb throttle bores straight into the head ports. Besides, a 180 manifold has runners to direct the mixture.

FWIW, here's an exploded view of my homemade carb linkage:

http://memimage.cardomain.net/member...178_6_full.jpg