There is an equation which determines how many cfm a motor truly
needs. It is based on the displacement and redline of the motor. The
max rpm of a motor is subjective, but myself, I personally don't rev my
'75 over around 5000 rpm. If you look at the stock curves for the '75, the
max hp is at 3800rpm and the max torque at 2200rpm.
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
On 2/23/02, at 7:59 PM, GLCurley@aol.com wrote:
>In a message dated 2/23/2002 7:15:58 PM Eastern Standard Time,
>alphachi@writeme.com writes:
>
>
>> My suggestion is to go with an Edelbrock replacement if possible, and not
>> too large (like 4v500cfm tops), with elec choke, vac. sec, yada yada.
>>
>
>500cfm is too small! I've got the Holley 1850 600 cfm (which was Terry's
>recommendation) on stock manifold of my 74. It was inexpensive and is very
>good performer. The orig carb was kind of junk, but I'm hanging onto it in
>case I need to get more "original" one day.
>
>George Curley #220, 670
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