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Old 09-06-2008, 08:23 AM
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Carb adapter

I am going to a new track to race and their rules state that you can only run a 2 barrel quadrajet on chevy engines. Rules also say that you can still run the 4 barrel intake with an adapter to accomplish this. Only problem is that I cant find one that I like. They say 1" spacer max, anybody out there know where I can find a part like this? Any help would be much appreciated.

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Old 09-06-2008, 08:46 AM
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I`ve only seen 1 two to four barrel adaptor, and it wasn`t very good. It was a open type with a lot of bad curves. I told my nephew not to use one on his demo derby car, he didn`t listen and did anyways, the engine came down from a high rev and due to the fuel puddling from all the curves and flat spots in the adaptor the low rpm vacuum sucked the excess fuel in flooding it out and he got nailed good and it wouldn`t restart. So they say you can only run a 2 barrel Dualjet carb? that sucks as the dual jet is the primary half of a Quadrajet and don`t flow much at all. GM did make some dualjets that had Quadrajet body`s. it was identical to a Q-jet but only had 2 barrels. Lastly, If you mean the old style 2 barrel GM carb they flow somewhat better than the dualjets, but I am unsure about a adaptor that works very well. If it were me, I would just swap over to a 2 barrel intake.
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Old 09-06-2008, 08:49 AM
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How much power is that gonna take away? i've been working them over but they just refuse to change the rules for me..lol
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Old 09-06-2008, 11:33 AM
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Quote:
Originally Posted by ragincajun19
How much power is that gonna take away? i've been working them over but they just refuse to change the rules for me..lol
It seems that a factory intake is mandatory?
I, too, think that a pure 2 bbl manifold is the proper way to go.
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Old 09-06-2008, 04:27 PM
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Good factory intake for 2bbls is a 1969 Canadian unit numbered 3916313
350ci @ 250hp and if you can, maybe look for a larger 2bbl from a school bus or a Vega/Monza with the good venturi cluster shooters that looked like Holleys. Sorry, no numbers, but, circle track people might be able to help. You might be pleasantly suprised at how much cfm they can/will flow and the power delivered at higher rpms... Ted
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Old 09-07-2008, 09:49 PM
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There is a special iron SBC 2 bbl intake the circle track boys use, I have seen them.
I am not for sure, but I think it is a GM marine intake. Out here they run a 500 2 bbl Holley on them.
I will try to find out tomorrow and report back.
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Old 09-07-2008, 10:20 PM
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Quote:
Originally Posted by ragincajun19
I am going to a new track to race and their rules state that you can only run a 2 barrel quadrajet on chevy engines. Rules also say that you can still run the 4 barrel intake with an adapter to accomplish this. Only problem is that I cant find one that I like. They say 1" spacer max, anybody out there know where I can find a part like this? Any help would be much appreciated.
Are you limited to a factory 4 barrel manifold or can you use an aftermarket?

Further are you limited to a 2 plane manifold or will they allow a single plane?

The best of factory SBC 4 barrel manifolds is easily eclipsed by the modern aftermarket.

Are there any rules preventing you from making your own adapter?

Adapters are easy to make and with a little experimentation you can usually make one to flow better. A couple rules to keep in mind with air flow:

1) You don't want it just wandering around in the hopes that it will find its own path, it won't, at least not with much efficiency.

2) Harsh changes in direction cost energy. This is a corollary to number 1 above, but adds certain trim factors. For example, the lower plane of a two plane manifold always flows less, as much as 20% less, than the upper plane. So there is plenty of space to think about whether the shape and size of the side feeding the lower plane should be the same as the upper plane side.

Remember, like Smokey always said, "if the rules don't expressly forbid it, then doing it is fair play". So look at the rule book with your thinking cap on.

Bogie
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