Plenums

[Bob Wooten]

I think that there is a point when the plenum can be too small for the air
that the motor wants to pull @ WO.  if i am not mistaken this is why
Lingenfelter made the box (super ram).  he was running a 383 in the silver
state classic & he somehow figured out that @ speed the motor was sucking
the plenum out of air & that by making a bigger box that it did not do that
any more.  i would expect that w/forced induction this would not happen but
in naturally aspirated it could.  comments?  is there something to this or
was i caught up in the bigger is better, sales propaganda?

Bob Wooten


> [Original Message]
> From: Bruce Plecan <nacelp at bright.net>
> To: <gmecm at diy-efi.org>
> Date: 1/15/01 4:11:47 PM
> Subject: Re: Plenums
>
> 
> 
> > Why is it desirable to have the plenum volume the same as engine
> > displacement?
> 
> I started measuring all kinds of volumes, some years ago.   First started
> with some ram air experiments I was doing.  Over time, it just worked out
> that for what I liked the closer to CID things were nicer, was a gray
matter
> until I built a incar timer and then it started to show actual performance
> gains.   A 1/4" spacer under the lid of a Crossfire just changed it's
> personality entirely.
> It allows the air to lose ineritia and bend around to fill the runners
> without having to lose energy.
> 
> > If the plenum volume is less, what are the bad things that happen?
> 
> At lower rpm, keeps the column moving as more of a column, and helps with
> low rpm cylinder filling.
> 
> > If the plenum volume is more, what are the bad things that happen?
> 
> I've seen some stuffup at 1.5xCID, and no down sides, at speed.
> You might have some **laziness** off of idle but I don't *drive* there.
> I personally think it's used as a way to better optimise the *tune* for
> emissions (keeping it small).
> 
> > I know I'm going to regret asking this but what functions does the
plenum
> > perform?
> 
> It just is where runners meet.
> Basically, you have
> IR   Individual Runners
> Single Plenums
> Dual Plenums
> Variable Plenums
> 
> > Does the Bosch book discuss such things for plena and runners?
> 
> My turn what's a plena?.
> Bruce
> 
> 
> 
>
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--- Bob Wooten
--- r71chevy at earthlink.net
--- www.r71camaro.homestead.com 


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