will a squarebore to spreadbore adapter plate effect performance?

lime4x4

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The manifold i got for my vortec engine is a dualplane squarebore carb setup. I want to use my quadrajet for the time being and that's a spreadbore. I have a 1 inch thick adapter plate that will allow me to mount the quadrajet. Will this cause any performance issues?
 

mylesm260

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Re: will a squarebore to spreadbore adapter plate effect performance?

90% of older chev small block and V6 manifolds are already poo by design.

Here's a simple way to check if it's going to effect performance:

Does the manifold/adapter plate combination have a smaller opening than the 4 barrels on the carb?

So long as you're not introducing a restriction, it should be okay.

In fact, in a lot of cases, introducing a spacer can actually help performance.
 

Rat Capri

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Re: will a squarebore to spreadbore adapter plate effect performance?

The manifold i got for my vortec engine is a dualplane squarebore carb setup. I want to use my quadrajet for the time being and that's a spreadbore. I have a 1 inch thick adapter plate that will allow me to mount the quadrajet. Will this cause any performance issues?

as long as it's not an open spacer you'll be fine, will probably have to adjust idle a/f mixture slightly
 

MikDee

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Re: will a squarebore to spreadbore adapter plate effect performance?

dont use that one, the engine will idle like **** and run like **** anything under 3/4 throttle, get a 4-hole spacer and the proper gaskets.

I don't see anything wrong with that spacer? Why do you think they even make it, if it's gonna be a problem? Plus, usually an increase in plenum height is advantageous, because it gives a longer runner to the manifold, usually increasing torque.
 

alumi numb

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Re: will a squarebore to spreadbore adapter plate effect performance?

don't know about that one but i used a 4 holer and then took a die grinder to the intake so the holes funnel smoothly.
don't remember what brand as it's been some time now.
different engine and manifold, 390 amc and offy 360 dual port.
crane cam and lifters plus doug thorley headers
built to be a mid range engine and runs i think great.
1968 amx with only 53k miles on the o.d.
sets in my sons garage now and is his.
when he was in iraq he asked me how the amx was doing.
i asked him if he wanted it, quick reply h*** yes!
then i told him all you have to do is come home alive and it's yours.
i think i got a bargan.
opps, sorry but that's how i matched a spread bore double pumper.
 

a70eliminator

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Re: will a squarebore to spreadbore adapter plate effect performance?

Cool car, Mark Donahue come to mind. that spreadbore adapter will just fine you probably wouldn't feel the difference.
 

Bondo

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Re: will a squarebore to spreadbore adapter plate effect performance?

The manifold i got for my vortec engine is a dualplane squarebore carb setup.

Ayuh,... I agree,... Why would you want to put an Open plenum over a Dual Plane manifold,..??
 

lime4x4

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Re: will a squarebore to spreadbore adapter plate effect performance?

it's not going to stay that way.. In a month or so i want to replace the quadrajet with an Edelbrock 1409 in a month or so
 

Rat Capri

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Re: will a squarebore to spreadbore adapter plate effect performance?

I don't see anything wrong with that spacer? Why do you think they even make it, if it's gonna be a problem?

it's not a problem if yhe engine stays above 4500 rpms all the time

Plus, usually an increase in plenum height is advantageous, because it gives a longer runner to the manifold, usually increasing torque.

that's only true if velocity increases or at least stays the same, that's not gonna happen with that open hole spacer......should only use a spacer for the manifold type you're using
 

MikDee

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Re: will a squarebore to spreadbore adapter plate effect performance?

Personally, I don't think it matters one way or the other :rolleyes:
 

mkast

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Re: will a squarebore to spreadbore adapter plate effect performance?

From Dennis Moore:

CARBURETOR TO MANIFOLD ADAPTERS
When General Motors' Rochester Division decided to quit making the
Quadrajet carburetor, Mercruiser switched to the Weber carburetor.
Unfortunately the Quadrajet four barrel is a spread bore design
carburetor and the Weber is a square bore. All Chevrolet marine engines
with standard performance intake manifolds have the Quadrajet spread
bore carburetor mounting flange. An adapter is used by Mercruiser to
mount the square bore Weber carburetor on the spread bore manifold. This is not an ideal situation, to say the least, for maximum performance. The Rochester Quadrajet is one of the finest carburetors ever built It has
been discontinued because the entire automotive industry has converted to
fuel injection. Purchasing a used Quadrajet marine carburetor from a
Boat dealer and installing it in place of the Weber,and doing away with the
adapter,would be an excellent idea. The Weber four-barrel is also an
excellent carburetor. Installing a square bore intake manifold while
retaining the original Weber carburetor would be another good
option in order to do away with the adapter. Either way,getting rid of the
adapter should be one of your first steps for increased engine
performance.
 

Bondo

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Re: will a squarebore to spreadbore adapter plate effect performance?


Ayuh,.... Actually,.. This would be the Best adapter to use,...
1409.jpg


You're gonna change it in a month or so,...
Break out the plastic,+ do it Right the 1st time,.....;)
 

Bifflefan

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Re: will a squarebore to spreadbore adapter plate effect performance?

for all the nay sayers,
When you put on a spacer of any kind you are increesing the plemtem space and that is always a good thing. thats why in racing they limit you to a 1 inch spacer. as for the open spacer to the duel plane intake it does change the flow abit but you wont see any problem with it. these have been around for many many years and have done fine. now if you have a racing motor and are trying get the very last single HP out if it then things are different and i can write about that all day long, and well into next week. as i havent read anything about it being more than a stock engine (meaning it doesnt make more than 50 more hp than the factory model) then you will have no problems at all with that adapter. if fact it will run better in the top end, without a noticable gain or loss at off idle.
Hope this helps. i guess 25+ years of racing didnt hurt after all.
 

kevincave

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Re: will a squarebore to spreadbore adapter plate effect performance?

this post could go on forever with opposing arguments. i would think you would need dyno data to backup any of these arguments....kc
 

mylesm260

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Messages
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Re: will a squarebore to spreadbore adapter plate effect performance?

See, this is why, when I used my truck vortec motor, I did this:
 

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lime4x4

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Re: will a squarebore to spreadbore adapter plate effect performance?

Bondo i don't do PLASTIC
 
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