Carb selection for repower project

84EdH

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I am putting a 5.7L vortec in my old 1979 Century 3000. The intake manifold is a spreadbore cast iron manifold sold by Michigan Motorz. I have an old Rochester Quadrajet, but needs an electric choke conversion. This seems simple, but in truth, I had so much trouble last season with my old engine, I am nervous about using this old carb on my new project.

considering a new carb purchase: is an Edelbrock 1409 with a square hole adapter a good choice, or should I try and find a new spreadbore carb with no adapter? I am not building a race engine, just typical boater. Faster is better, pull kids on tube, slalom skiier.....looking for reliability foremost.

thanks

Ed
 

odie241

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May 17, 2010
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Re: Carb selection for repower project

I re-powered my 1977 thompson with a 400ci chevy,I used an edelbrock carb,and also an edelbrock intake.I love them,they are pretty much take them out of the box,hook up the throttle,ect,and go,very minor adjustments needed.Heres a pic of my set-up.
30265_1447600150601_1251100943_1-1.jpg

I used all the parts off the 898.they bolted right up with no issues
 

84EdH

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575
Re: Carb selection for repower project

nice looking set up! Edelbrock makes only a square bore carb to my knowledge. Are there any negatives to buying the Edelbrock 1409 and using an adapter to cover the spreadbore intake? or is hunting up a spread bore carb a better idea?
 

mkast

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Re: Carb selection for repower project

Dennis Moore's marine small block Chevy book states using an adapter plate will disrupt air flow.
Although, I have seen Mercruiser use an adapter plate on a 310 horsepower 454.
 

wca_tim

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Re: Carb selection for repower project

I've run several edelbrock carbs with a carb adapter, etc... no problems. plugs read consistently from one cylinder to another. you night also consider updating the intake it's worth some horsepower for reasonable money if you choose right.
 

Mike220

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May 4, 2011
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Re: Carb selection for repower project

My 1997 5.7 LX merc uses a high-rise spreadbore manifold with the Weber squarebore carb. The Edelbrock 1409 is identical (I think) to the Weber. It does have a very thin adapter plate on it.
 

84EdH

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Re: Carb selection for repower project

I am using some parts from a 1995 Mercruiser 350 Mag parts engine. It used a Carter carb (that was square bore) with an adapter plate bolted to a cast iron spread bore intake, with a mechanical choke. This was all stock. So, I am sure it works. I am just trying to put the best combination together now.

I did update the manifold with this high rise, spread bore cast iron manifold from Michigan Motorz.......before I realized that I needed a carb with an electric choke. The manifold is already bolted on. Here is a picture of it:

http://www.michiganmotorz.com/vortec-cast-iron-intake-manifold-1996current-p-465.html

Any spread bore carb reccommendations? This is a 5.7 marine vortec long block with no EGR and needing an electric choke.
 

84EdH

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Re: Carb selection for repower project

yes it accepts both types.......but with an adapter plate....the issue is whether the adapter plates cause any problems.

also, this IS the performance update manifold (or so I thought) I now own this manifold and am searching for best carb for what I have now. thanks all for suggestions
 

mkast

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Re: Carb selection for repower project

yes it accepts both types.......but with an adapter plate

When there are eight holes for mounting the carburetor, the intake manifold will accept both square bore and spread bore carburetors, without an adapter.
 

FreeBeeTony

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May 15, 2002
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Re: Carb selection for repower project

When there are eight holes for mounting the carburetor, the intake manifold will accept both square bore and spread bore carburetors, without an adapter.

That's what I was refering to.......
 

84EdH

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Re: Carb selection for repower project

Well maybe I am confused (not first time). When I spoke to Edelbrock, they recco. the 1409 which is square bore. They said I needed an adapter plate to put on my spread bore manifold. Never asked me if it was four or eight bolt setup.
 

84EdH

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Re: Carb selection for repower project

I am still hoping to get some info. on this "adapter plate" issue. I have an adapter plate that fits over a spread bore manifold, that closes in the hole sizes. I assumed this is necessary to make the square bore carbs operate better on the spread bore manifolds. Just being able to attach either carb type to my manifold doesnt seem to be addressing my question about performance.

Should I get a spread bore carb to work with my spread bore manifold, or can I use an Edelbrock 1409 with an adapter plate that closes the hole size on the secondarys in?

Help appreciated !
 

dan t.

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Re: Carb selection for repower project

First,the adapter plate, yes they do disrupt air flow but going from square to spread is better than the other way. One thing to consider, is the adapter open or divided, an open adapter will decrease bottom end and increase top end power,best to use an adapter with a divider. Why not just get a rebuilt exchange Q-jet, far better carb,it will give you better fuel economy and throttle response and it matches your manifold.
 

FreeBeeTony

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Re: Carb selection for repower project

Why not just call MichiganMotorz and ask them if the 1409 will work w/o an adapter plate.......
 

dan t.

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Re: Carb selection for repower project

Something just popped into my head, when you install the intake I strongly suggest you use the Felpro aluminum based intake gaskets. The stock plastic based gaskets are very prone to failure after a couple of years. Spend the extra bucks and only do it once.
 
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