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Old 07-15-2007, 04:52 PM
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Dual Quads

On a early SBC(50-60's) dual quad system I assume that the rear carburetor operates all the time and the front carburetor comes in after half throttle or so. My question is there an imbalance between cylinders do to the distance of the rear carburetor to the two front cylinders? Would it be safe to have the front carburetor just use the idle circuit and just run normally off the rear carburetor?
Thankks - Jerry
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Old 07-15-2007, 05:24 PM
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Jerry, it's an imperfect world and as long as we are using carburetors on a motor, it won't be anywhere near perfect. In my opinion, as good as it gets currently is a computer-controlled fuel injection system with with injectors in each head port and equalized runner lengths.

Us hot rodders have been trying to perfect carb systems since the turn of the last century, with a moderate amount of success in some cases.

In my opinion, with the motor under little load at idle and the small amout of mixture that would enter the motor from the secondary idle circuit at higher engine speed, it wouldn't make a whole lot of difference. But hey, go ahead and try it if it will make you feel better. Nothing hurt except your wallet, paying for lower fuel mileage.
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Old 07-16-2007, 01:44 AM
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Quote:
Originally Posted by fred56

On a early SBC (50-60's) dual quad system I assume that the rear carburetor operates all the time and the front carburetor comes in after half throttle or so. My question is there an imbalance between cylinders do to the distance of the rear carburetor to the two front cylinders? Would it be safe to have the front carburetor just use the idle circuit and just run normally off the rear carburetor?
The last one I saw was a 58 VETTE...

The rear carb (now I am more familiar with FORD so bear with me here)- Is the Primary Carburetor, i.e. it is used mainly for normal street operation. The front carb is referred to as the Secondary Carburetor and is used only when more performance is wanted.

Being a Dual Plane intake manifold, the engine can operate off the primary carb smoothly as there is a common plenum. The carbs will be reversed whereas the Primary Carb primary venturis are about mid-plenum to deliver fairly consistent delivery in normal driving. The Primary Carb primaries are linked to the Secondary Carb primaries by use of adjustable solid linkage whereas the cut in of the Secondary Carburetor can be controlled to driver needs/wants. Of course the secondarys are vacuum actuated and they can be adjusted to come in at whatever manifold vacuum is desired (or mechanically actuated for hot street/track). A nice trick is to use connecting vacuum signal secondary motor tops to tie the two vacuum motors together so they will open at the same time.

The Secondary Carb idle, power and enrichment circuits are vital to smooth street operation.
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Old 07-16-2007, 12:23 PM
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didn't weber or someone make a one carb/cylinder induction system? It'd look sweet and run sweet once it got tuned right. But that would take a looooooong time!
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Old 07-16-2007, 01:24 PM
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Old 07-16-2007, 03:42 PM
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Dual Quads

I'd love to have the webers but my pockets aren't deep enough. Thanks for the info on the linkage operation.
Jerry
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