plenum volume

[jb24 at chrysler.com]

Optimum plenum volume is a case-by-case basis.  Just like exhaust
tuning, intake tuning (which includes all runners and the plenum) will
generate different characteristics depending on application.  Their are
two modes that are involved.  The first is called organ-pipe, which
have straight runners and no plenum (or very large plenum).  The runner
length will generate positive pressure pulses at a certain rpm band and
boost VE.  It will also generate pulses at multiples of this rpm, but
that is usually outside the operating range.  The second type is called
Helmholz tuning which includes a plenum volume as part of the
"resonating" system.  A Helmholz intake resonates (generating positive
pressure pulses) at TWO rpm bands and multiples thereof.  You can fiddle
 with runner lengths, plenum volume and plenum inlet length to fill the
holes in your torque curve this way (keeping your flow bench nearby so
that your magical combination doesn't also happen to be restrictive).
Additional plenums get hung off the intake to cancel intake noise, but
usually performance engine types like noise.  Several SAE papers and
engine design books describe how to do this.

John Bucknell is jb24 at chrysler.com
---------------------- Forwarded by John R Bucknell/JTE/Chrysler on
02/20/98 01:27 PM ---------------------------

        owner-diy_efi @ efi332.eng.ohio-state.edu
        02/20/98 03:10 AM
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Subject: Re: plenum volume

HI
In the Bosch CIS/CIS-E (note continuous/non-timed injection) manual they
state that the optimum volume for the runner between valve and plenum
should
be equal in Volume to 1.5 times the cc of the cylinder it feeds. Their
idea
is that the backwave when the valve slams will not push the air/fuel
charge
back into the plenum and disturb the cylinder to cylinder a/f ratio.
This
is kinda hard to do on a V8 as anyone who looked under the hood of a
Porsche
928 can observe. Big ole tarantula sitting in the valley.

At 11:52 PM 2/19/98 PST, you wrote:
>ref Paul Tholey:
>   IMHO, for a SBC runners should be thought of more in
>this manner.
>   Large cross sectional area runners are for better cylinder filling
at
>       high rpm.
>   Shorter runners enable a motor to rev quicker.
>   Long runners help to minimize reversion.  Reversion
>   can truely hinder MAF readings.
>(needless to stay the inverse apply)
>So a vehicle with a wide ratio gear box, and lower
>   (numerically) gears would need to min reversion
>   (long runners), and would not need to change rpm
>   quickly.
>Part of the reasoning for this is the Can-Am big blocks
>of the mid/late 60's, really long IR with huge cross-
>sectional areas.
>  It sorta follows the flow, of what most people do/think
>but I like my tweaks.
>  Bruce
>Any others with other thoughts?.
>
Lotsa Luck Eric
85 GTI with VR6 power