4bbl or BIG 2bbl
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4bbl or BIG 2bbl
-Hey guys, the stock 2bbl carb on my 351m has go to go. It stutters and won't set right. 
I saw in the Jegs catolog a selection of 2bbl carbs that go up to 600 CFM! The reason why is that I can get a Holley 500cfm 2bbl carb for less than half the price of a 4bbl and manifold, and it's a direct Ford boltup! Do you think it will be effective with the stock manifold? Even if it's not though, it'd be a heluva improvement from what's on it. 2 barrel, or 4 barrel, 2 barrel, or 4 barrel...hmmmm
So if you guys got any PROS / CONS,
let me know- I like opinions.
-Dan
:-X11
I saw in the Jegs catolog a selection of 2bbl carbs that go up to 600 CFM! The reason why is that I can get a Holley 500cfm 2bbl carb for less than half the price of a 4bbl and manifold, and it's a direct Ford boltup! Do you think it will be effective with the stock manifold? Even if it's not though, it'd be a heluva improvement from what's on it. 2 barrel, or 4 barrel, 2 barrel, or 4 barrel...hmmmm So if you guys got any PROS / CONS,
let me know- I like opinions.
-Dan :-X11
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4bbl or BIG 2bbl
-Well it is an option, but not one I want to take. I've had carbs rebuilt before and then leave me on the side of the road. And I never used the same shop twice. I figured I'll up the cfm and get a 4bbl and manifold along with a cam. Then I ran across the 500cfm 2bbl. If I get a cam but leave on the stock manifold will it be effective?
-Dan
-Dan
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From: Gravel Switch, KY
4bbl or BIG 2bbl
I have heard this all my life and cannot prove it to be true but it does make sense. The smaller the venturis in a carburetor the higher the air velocity will be which results in a stronger metering signal to the boosters and better atomization of fuel. This is the principle behind the 4 barrel carb. The 2 small primary venturis will help fuel economy and driveabilty while the secondary venturis are there for when you put your foot in it and the engine requires more fuel than the primaries alone can provide. A big 2 barrel would not be as good for economy as the 4 barrel due to the velocity being lower at lower throttle openings. The velocity is lower on the big 2 barrel because the venturis have to be large enough to flow the all the cfms the carb is rated for. As I said, I have never proven this true myself, probably because whenever I put a 4 barrel on something it is because I want to flog it and the gas mileage sucks anyway. 
Does this make sense?
DannyP
Does this make sense?
DannyP
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4bbl or BIG 2bbl
>The smaller the venturis in a
>carburetor the higher the air velocity will be which results
>in a stronger metering signal to the boosters and better
>atomization of fuel. This is the principle behind the 4
>barrel carb. >openings. The velocity is lower on the big 2 barrel >because the venturis have to be large enough to flow the all the
>cfms the carb is rated for.
Sounds like a large 2bbl would also hurt low RPM acceleration. Never thought 'bout that
I suppose it's worth the extra money gas wise to use a 4bbl. That's fine thought gives me a good reason to go all-out 
-Dan
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4bbl or BIG 2bbl
Years ago I had a 500cfm 2bbl carb on a 69 mustang with a 351W that ran like a scalded hog. I receantly built a 351W and used a Holley 650 and it runs good but not as good as the 2 barrel did. I don't know what to conclude but have read lots of books on choosing the right carb size. From what i can tell almost every carb on a home built engine is too big. A too big carb gives sluggish throttle response and that is exactly how i would describe the latest 351w i just built. The mystry continues.........
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