Holley 6212 AAA 800 cfm Spreadbore - ClassicOldsmobile.com


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Old April 15th, 2018, 06:16 PM   #1  
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Holley 6212 AAA 800 cfm Spreadbore

I was thinking about shopping for 1 to try out. I know that they are no longer making it so I would be looking for NOS or used. Has anyone used it before? So that I may learn from your experience before going down this route.


Thank You ahead of time.
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Old April 16th, 2018, 07:18 AM   #2  
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I ran one of these spreadbore Holley carbs years ago. Don't waste your time. Get a properly built and set up Qjet. Your car will thank you.
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Old April 16th, 2018, 08:17 AM   #3  
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My old man had a spreadbore Holley on his 71 Corvette with stock 350.

It did a couple things differently.

The Holley would not let fuel evaporate so much, and the QJ required more cranking when sitting for a while.

The QJet did not load up while idling which the Holley did.

The Holley had mechanical secondaries and you would feel the boot of the gods when they kicked in; the Qjet was more smooth.

The Holley would let the car do 135 all out, and the QJet allowed 125, circa when new, 1972.
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Old April 16th, 2018, 08:25 AM   #4  
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Old April 16th, 2018, 10:19 AM   #5  
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The Holley had mechanical secondaries
So does the Qjet. Adjusting the spring wrap on the air valve and dialing in the orifice on the dashpot will give you the same feeling.
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Old April 16th, 2018, 10:46 AM   #6  
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So does the Qjet. Adjusting the spring wrap on the air valve and dialing in the orifice on the dashpot will give you the same feeling.
I wasn't precise enough. The Holley did not have the vacuum air horn valves the QJet has. Mechanical secondaries, in my terms, means the whole back two barrels, not just the throttle blades.
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Old April 16th, 2018, 10:50 AM   #7  
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I wasn't precise enough. The Holley did not have the vacuum air horn valves the QJet has. Mechanical secondaries, in my terms, means the whole back two barrels, not just the throttle blades.
The Qjet has mechanically operated secondary throttle plates, period. The air valves obviously open in response to mass air flow through the secondaries, but they can be adjusted to preclude any added resistance. If properly adjusted, this will not be a performance loss.
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Old April 16th, 2018, 11:22 AM   #8  
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What are you going to use it on? What manifold?
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Old April 17th, 2018, 05:55 AM   #9  
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I was thinking of using it on our W-30 so that I wouldn't have to alter the factory carb. Our car currently has the Sig Erson Hy Flow2 cam in it with the stock intake. Not really wanting to change the intake. I have use the Holley 650cfm Spreadbore in the past and really like it. That is why I was thinking of the 800cfm on the stock intake.
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Old April 17th, 2018, 06:04 AM   #10  
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That one on eBay looks good. If you are familiar with them, grab that one. The factory W-30 carb is only 750 cfm, mods like adjusting the air door to open more might help.
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Old April 17th, 2018, 06:26 AM   #11  
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Its hard to compete against a quadrajet and I don't think you'll gain anything. With that said the Holley 6212 is a good carb compared to its 6210 counterpart.
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Old April 17th, 2018, 12:40 PM   #12  
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The Qjet has mechanically operated secondary throttle plates, period. The air valves obviously open in response to mass air flow through the secondaries, but they can be adjusted to preclude any added resistance. If properly adjusted, this will not be a performance loss.
I don't know how it did it, but the Holley made the engine jump harder.
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Old April 17th, 2018, 03:52 PM   #13  
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I try one on my car never took it off run better then any Qjet and easy to tune.
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Old April 17th, 2018, 03:53 PM   #14  
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I agree with Old Cutlass,if prepared by someone who understands Q-jets and knows their faults,they are an awesome and trouble free carb.However the Holley spread bore is also an awesome carb,I have built many with never a problem.I have three in service in my own vehicles right now.When building a Holley you must be surgically clean as they will tolerate ZERO foreign material.If you choose to go that route,I have several of them if interested
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Old Yesterday, 04:34 PM   #15  
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If you choose to go that route,I have several of them if interested

While that Carb on Ebay looks temping, I don't like working with Ebay and do not have the means to do so.


When you say several, what kind of shape and condition are we talking about? PM me if you would like to keep personal information safe.
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Old Today, 03:01 AM   #16  
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A major thing to consider is that Quadrajets were federal emission carburetors so they had precise idle and cruise fuel metering. Off the shelf Holleys could dump as much gas as they wanted and worked better on modified engines. Quadrajet idle/cruise circuits can me modified for high performance engines and give great throttle response. Check out this video as proof.
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