Upgrading a 2 barrel Rochester to a 4 barrel

MannyV17.1

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Jun 6, 2010
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I have a 3 litre GM OMC with a 2 barrel Rochester Carborator and I am looking to find out if anyone has converted their engine to a 4 barrel Carborator in order to increase horsepower. Any thoughts or suggestions ????

I was thinking of a 4 barrel of approx. 490 CFM for this 180 cubic inch engine. Too much?, will it flood?, will I gain horsepower?

other alternatives?
 

Bondo

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Apr 17, 2002
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Re: Upgrading a 2 barrel Rochester to a 4 barrel

will I gain horsepower?

other alternatives?

Nope,...

Not really....
 

zbnutcase

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Sep 19, 2009
Messages
2,055
Re: Upgrading a 2 barrel Rochester to a 4 barrel

350 cfm Holley marine carb is the max I would do on a stock 3.0-if I bothered at all. Only pencils out if you need a new carb anyway.
 

Bifflefan

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May 27, 2009
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2,933
Re: Upgrading a 2 barrel Rochester to a 4 barrel

Id call that a drowning, not an upgrade.
Upgrades make things better, and that wont.
 

fossill

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Jun 20, 2009
Messages
427
Re: Upgrading a 2 barrel Rochester to a 4 barrel

Yup, probably make more sense to put a 1 bbl carb on it than a 4. But that's a down grade too.
 

45Auto

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May 31, 2002
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2,842
Re: Upgrading a 2 barrel Rochester to a 4 barrel

As others have said, a 4 barrel carb will not make any difference on your 3.0L. Any internal combustion engine is a pump, it sucks air in and pushes exhaust gases out. The carburetor on your engine is NOT the choke point that is restricting the flow through your engine. Essentially the same carburetor is used on the 4.3L, the 5.0L, and the 5.7L. One of the members here just replaced the 2 barrel on his 5.0L with a 4 barrel, you can see his results on this thread:

http://forums.iboats.com/showthread.php?t=396275

If you don't feel like reading the thread, I can summarize it for you: it made no difference at all.

He was also using a manifold designed for a 4 barrel, not some hodge-podge of adapters like you would be forced to use on the 3.0L.
 

MannyV17.1

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Jun 6, 2010
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Re: Upgrading a 2 barrel Rochester to a 4 barrel

Well I guess I have my answer.
Thank's guys.
I just posted my question this morning and now I have a whole lot of info.
Thanks also for the thread refferal.
So, to better be able to do all the skiing with a boat full of people I guess I should invest in another prop rather than carb since it isn't going to give me any power increase.

Yes, thank you all again.
 
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