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Old 04-09-2012, 07:14 PM
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Spread bore manifold & square bore carb?

Friends car. Heres the situation. 1981 camaro slightly modified. It has the original intake manifold (GM spread bore) and original carb (Q-jet). The carb is in dire need of some serious tuning...... other option is swapping out the carb for the other carb I have which is a fairly new Holley 670 street avenger (square bore). Question being is the Square Bore 4150 style holley carb compatible with the stock Spread Bore GM intake manifold? I have read conflicting data stating that you can mount a square bore carb to a spread bore manifold but not visa versa? Or would it be more advisable to just remove the Q-jet, clean it up and get it properly tuned? Would rather put the Holley 670 on there just not so sure that it would bolt on to the spread bore manifold............


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Old 04-09-2012, 07:23 PM
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The only way the holley will bolt on is with a adapter plate and you don't want to go that route. Adapter plates belong in the trash. They disrupt flow, cause tuning headaches and disrupt the vacuum signal. Get the Quadrajet serviced correctly and it'll be fine. Going by what you said I see you would rather use the holley, but thought I should say there is no better street carb than a Quadrajet. The Quad is rated at 750 cfm but it's a air dam carb, meaning it delivers what the engine demands, no less no more. If both carbs were tuned correctly and dyno tested on the same engine you would see the holley doesn't deliver anymore power than the Quadrajet does. When a Quadrajet is right for the combo, it's small primaries deliver real sensitive fuel injection like throttle response and when wide open power is needed the massive secondaries come in a deliver all the fuel demand the engine needs.
It could be simply your not too Quadrajet savvy as it looks complicated but it's not. Once you learn a Quadrajet you find they are no more complicated than any other carb.
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Old 04-09-2012, 09:21 PM
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The only thing I will add to DoubleVisions declaration of carburetion is that, you can't do what you are asking the bolt holes are different, so you cannot just swap a squarebore in a spreadbore's place. Weiand does make intakes that will direct bolt both types of carbs (it has two different bolt hole patterns to choose from).

Here is an example: http://www.summitracing.com/parts/WND-8126/
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