[general145]

I was thinking about running a dual carb set up n my small block and was wondering what the best one is? I don't want a tunnel ram, i just want a low plane mainfold, set up for 2 carbs.
thanks

[davidpozzi]

Edelbrock makes one for dual inline carbs that is very compact but is a very old design with very short runners.

The other choice is a crossram dual four similar to the Z/28 factory crossram.
Offy still sells their version the base looks like it came out of the same molds as the GM unit. The top is similar but just a little different with OFFENHAUSER cast in the top in two places. It has different throttle linkage provisions too.

Edelbrock has a crossram version that is very similar to the offy/GM unit but smooth on the top, no ridge like the OFFY unit. It's no longer in production but used units are around.
All three units are within a half inch on height and width.

The GM version made 20 hp and 20 ft lbs more than a Z/28 single four manifold on a trans am race engine test.
I believe that a current Edelbrock (victor type?) single four manifold would make as much or more power.
A recient David Visard article using a single four manifold vs a tunnel ram showed the tunnel ram just edging the single four.
This was on a street SB engine.

There are the old ram log type high crossrams made by Edelbrock and Weiand. They are kinda high. They were replaced by the tunnel rams for racing.

I'm not aware of any other dual four setups.
CRG site below has a good article on the Z/28 type crossrams. http://www.camaros.org
David

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67 RS 327
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[This message has been edited by davidpozzi (edited 07-23-2000).]

[general145]

Thanks david,

The reason i was looking for a dual carb set up is not for performance gains but better gas mileage. I friend of my had a 57 chevy and ran one 750 carb on it then later switched over to 2 500's and he said he nearly doubled his gas mileage. Is there any validaty in that at all?
thanks

[gheatly]

The last reason on earth to change to two four barrels is better gas mileage. I don't know what your friend was smokin' when he told you that, but it's not true.

In my younger days, I had two Carter Competition Series 625 cfm carbs on an Offenhauser "dual port 360" 2x4 intake. I got around 11 MPG. Granted, the 625s are larger than 500s, but the carbs are designed to feed the engine based on demand. Therefore, I don't think you would get any better mileage with 500s vs 625s.

A single 4 bbl on a dual plane intake is the most efficient induction package. From what I have read and heard, the GM Quadrajet is the most miserly 4 bbl carb ever made. As with ANY carb, proper tuning is the key to performance OR gas mileage.

[Jeff H]

IF your friend was using dual 500's, he most likely had 2 - 2 barrel Holleys, not 2 - 4 barrel Holleys. You may want to consider one of the tri-power setups where you run off the middle 2 barrel and the other 2 only open up when the engine demands it by vacuum.

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Jeff H - 93 Indy 500 Pace Car, Hugger Orange 69 Z28 with JL8 brakes

[Jesses]

My $.02,

i had a friend that had a 60's vette that had a dual quad setup. i think that it worked off a progressive setup. it ran off the rear carb unless you mashed it, then the front opened up. unfortunaltely he no longer has the car and it has been 7 years since i saw it last. too long to remember what the linkages looked like. he got decent milage(granted that it was a light car to begin with), but i am looking at making either a tri carb motor or dual duece setup. i liked the look of the 6 pack on the "Grape Balls of Fire" on Horsepower tv. but then again i have a dual carb setup waiting for me already. i will probably go with dual 500cfm's like general's friend. with a total of 1000cfm, hope the economy primaries will keep the milage decent.



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[pdq67]

An old three-two setup with the little Rochester two barrel carbs like off a 1958 348 would be a good gas mileage combo, plus they look "tough".

Carbs off a 1966 Olds, a GTO, or even an old Olds J/2 setup back in 1957 will work. The front and back carbs on stock systems didn't have any idle screws in them and were mainly just gas "dumpers"

You drive on the center carb until you want to go, then the sound of the other two kicking in is "music to the ears".

I can still remember the sound of a buddy's 11 to 1 cr .060" over 292 "Y-block" 1956 Vicky Ford with a Z-30 Isky solid cam (I think), Hedmam headers, continental glas-pak's and three stromburgs. When the three two's kicked in, it made for a great ride.
pdq67

[CORNHOLIO]

I myself would just run one. My one gives me enough to work on and tune, let alone two and fumbling with linkage to open at the same time. I dont think you will get better milage running two. Twice the money for the carbs.