Like the post below on what CFM carb, what is the CFM of the stock 2BBL?

[reamer]

I Have the stock 2bbl and stock engine too, just picked up a Prefromer 289 4bbl intake. But wondering What is the CFM of the 2bbl compared to a 500 cfm 4 bbl?
reamer

 

[Broncobowsher]

I believe the 2V motorcraft is rated at 369CFM @ 3" Hg while the 4V is rated at 500 CFM @ 1.5" Hg. Here is one that will confuse most people, how do you get a 500 CFM carb to flow 750? Easy, test it with 2V pressure drop specs instead of 4V. carburators don't have a magical wall where they only flow so much. Flow is based on the pressure drop. 2V carburators are tested with a standard 3"HG drop between inlet and outlet. 4V 1.5"HG. But keep in mind that any vacuum in the manifold is a lack of pressure that could be filling the cylinders. If you look at the magazine carburator shootouts the bigger one is almost always the most powerful one. simply because it lets the most air in and does not create a pressure drop. But for most of us the drivability at less then max flow will trump the tiny flow gains on the upper top end. Too big and you loose velocity and the high velocity of smaller carburators is what makes them run good for drivability.

 

[reamer]

Soooo for street drivability (and mileage) stay with the 2 bbl?

 

[Doyle]

Reasonable sized four barrel will actually improve low end because you're only on the primaries at low RPM, which equates to higher volicities. With a vaccum secondary carb the secondaries won't begin to open till the engine needs the extra flow.

 

[blubuckaroo]

Ford used a 2bbl carb for lots of big motors. My dad had a '74 F-150 with a 390 2bbl and used it to pull cotton trailers to the gin. That was a wicked torqy truck! Ford engineers may have known more than us guys who think it needs a 4bbl.