350 idle air consumption?

[Greg Hermann]

>Hey listers,
> Anyone know an approximate value of air consumption (CFM) a typical 350
>would consume AT IDLE??
>
> I'm trying to size out some injectors - want to make sure I can provide
>a fine enough adjustment for a decent idle control...
>
> Thanks!
>
>-Bill
>
Air consumption is not the real issue. Prolly about 4 to 6 HP being made at
idle (friction, accessories, oil pump, water pump, fan, etc. Figure a bsfc
of about .44 #/bhp hr. @ idle (you want to be on the low side for this calc
to be safe.

So that gives you (4 HP/8cylinders)x .44 #/bhp hr.=.22 #/ hr. / cylinder or
injector. If your idle speed is 750 rpm, that means each revolution of the
engine at idle takes 80 ms and each cycle takes 160 ms [(60/750)x1000x2].
If you need, say, 32 #/hr. injectors to flow enough fuel for your top end
power, that means that your injector duty cycle at idle will be .22/32, or
.69%. And .0069x160ms/cycle would mean that the injector pulse width at
idle would be 1.1 ms--pretty marginally short to get repeatable amounts of
fuel in each squirt, prolly need peak and hold injectors to make it idle
really smoothly, plus hope the assumed numbers were a fuzz more to the low
side than in the real world, and hope that, for once, maybe your engine has
a bit more drag.

Regards, Greg
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