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Old 04-26-2007, 12:05 AM
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Carb adapter: 4 hole or open style?

I'm trying to decide which carb adapter would be best suited for my application. It's a chevy 350 in a 4x4 truck. I'm thinking about swapping the quadrajet for a edelbrock 1406 which is a square bore carb. So in order to put the squarebore on the stock manifold I need an adapter. Is there any performance difference between an open type spacer adapter vs a 4 hole adapter. For example, this:



vs



This engine is built for low rpm torque. It is not a high rpm, high horsepower build. I'm looking for something that will be most efficient for daily driving and low end power for towing and full loads. Will there be a difference between these two adapters?

Also, since I have your attention. Is the edelbrock 1406 a good choice over say a holley 1460? I'm a big fan of holley 4150 double pumpers for performance applications, but this is a daily driver and economy is a major concern. I've never used an edelbrock carb but they seem to have a lot of fans for street applications so I thought I'd give one a try.
Any help is appreciated,
dh
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Old 04-26-2007, 12:14 AM
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the answer is vague. Typically open spacers increase higher RPM hp since they increase the volume of the plenum. Four-hole spacers sometimes increase torque since they keep the velocity and sorta kinda increase the runner length. The confusion comes because some spacers hurt power when they should help, and some hurt torque when they should help. If I've learned anything from car craft and hot rod, its that you can't predict how a spacer will affect power other than past experience.

In general, I would suggest a four-hole spacer, but check first... chances are you don't need an adapter. Most spreadbore intakes are drilled with both carb bolt patterns. Pull the carb and see if the intake has 8 bolt holes. Putting a square on a spread intake is fine if that's the case. The problem comes when putting a spread carb on a square intake. The secondaries have to make such a radical transition to the plenum that it never works right, but no worries going from square carb to spread intake.
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Old 04-26-2007, 12:22 AM
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Quote:
Originally Posted by curtis73
Putting a square on a spread intake is fine if that's the case. The problem comes when putting a spread carb on a square intake. The secondaries have to make such a radical transition to the plenum that it never works right, but no worries going from square carb to spread intake.
That makes sense. I'll have to check my manifold. thanks,
dh
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Old 04-26-2007, 12:50 AM
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most likely you wont be able to put a squarebore on a stock gm intake. Id say if you got money for the spacer you got money to pickup a new intake at a swap meet or even new, it will be well worth it too. just my .02

Last edited by ChevyThunder; 04-26-2007 at 10:46 AM.
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Old 04-26-2007, 04:54 AM
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If economy is a major concern stick with the Q-Jet, get a quality reman from JET if you don't think you want to tackle rebuilding one. Otherwise I'd go with the 1400 Performer over the 1406, it is calibrated for fuel economy.


Quote:
Originally Posted by curtis73
. chances are you don't need an adapter. Most spreadbore intakes are drilled with both carb bolt patterns. Pull the carb and see if the intake has 8 bolt holes. Putting a square on a spread intake is fine if that's the case. The problem comes when putting a spread carb on a square intake. The secondaries have to make such a radical transition to the plenum that it never works right, but no worries going from square carb to spread intake.
I've never seen a factory Chevy Q-Jet intake with both mounting patterns on it.
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