intake plenum size?

[David Hunt]

Consider that on a larger (cylinder number) engine the runners to the other
cylinders perform as a plenum.  Oh, sure, there is action due to the last
valve that closed, but in general the other runners perform as a plenum.
So, lets see, If the head has 330cc in the intake runner, the intake runner
has 600cc and there are 7 other runners, then a small block Chevy has about
4,200 cc or 252 cu. in. of plenum in the other runners.  Then there is
another liter (guess?) just below the carburetor. So, on the venerable small
block Chevy there is a plenum just about the same size as the displacement..

Also, following Detroit's lead, as the performance goes up, probably due to
the closing rate of the intake valve, the plenum gets larger.

Don't idle? increase the plenum.  Look at the case of individual runner fuel
injection, like the old Hilbourn.  Infinite plenum!

I model the plenum (capacitor) as converting the pulsing flow of the intakes
(pulsed inductors) into a smooth flow for the carburetor.  This minimizes
the average pressure drop across the carburetor and increases the flow.

dh

----- Original Message -----
From: "Clare Snyder" <pop1881087 at mail.9netave.com>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, June 27, 2001 6:04 PM
Subject: intake plenum size?


> Just a quick question for you fellows - not fuel INJECTION related -
> There is an optimal "plenum" volume for an intake system. How is it
determined?
> Can't remember if it is the volume of one cyl, or twice the volume?
Something
> like that.
> Any formula, calculator, or rule of thum - please e-mail me and/or post to
the
> group
> This is for a carbureted system.
>
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