This is a good guideline but a little over simplified. Manifold choices come
into play, dual plane Manifolds 'hide' half the carb so they require a
larger carb than an open plenum manifold. Most street manifolds that 'work'
are, and almost all factory manifolds are dual plane. A 600 cfm carb works
fine on most engines of 327-383 ci. The Edelbrock carbs are a bit better
out of the box but more people know how to 'tune' holleys. My personal
choice is a 600cfm edelbrock, I've got one on my 360 dodge motorhome and it
has worked flawlessly right out of the box and for the last 3 years. The
motorhome is even heavier than the brick and it does not bog, burp or fart.
Rick.
> The equation is:
> CFM = [(cc's x RPM) / 3456] x VE
>
> if you assume a good stock motor volumetric efficiency of 85%, then the
> biggest carb you need is [(360 x 5000) / 3456] x 85%, or about 450cfm.
> Even assuming 100% VE, the number is still only 520. The bigger carbs,
> 600-750 cfm are needed when you've dropped a cam, heads, and manifold
> in there that lets you go to redlines of 6000+ rpm with better VE.
>
> a good site to visit which explains this maybe a bit better is
>
> http://www.mortec.com/carbtip1.htm
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