True, the momentum effect is not so great in a low pressure system (it
works phenomenally well using an aircraft engine bleed port, though), but
inertial extraction is still a factor. To summarize what RJ is pointing
out, the shock in a pipe occurs at the end. The pressure wave in
reflection turns negative instead of positive (the infamous Chester Smith
has great compressible flow writings as well if anyone cares to look
further). The low pressure local eddys will cause some residual exhaust to
be drawn out of the combustion chamber. The effect and geometry is
determined by the local speed of sound in the duct. It is still the
suction caused by the shock that gives you the advantage.
----------
> From: Randell Jesup <Randell.Jesup@scala.com>
> To: spridgets@autox.team.net
> Subject: Re: Exhaust Manifold vs. Header
> Date: Friday, May 01, 1998 12:56 AM
>
> "Ron Soave" <redlotus@spacey.net> writes:
> >My understanding: A header is a manifold that has pipe lengths and
> ...
> >are chosen so that there is what is sometimes called an ejector effect
(AKA
> >shock wave tuning or inertial extraction) where the pulse from one
cylinder
> >is timed so that the momentum of the slug of exhaust leaves an area of
low
> >pressure behind it that will cause an increase in intake charge during
the
> >overlap period (TDC) by "sucking" in more on intake (no Monica Lewinsky
>
> A minor point: that's a nice and very common idea to explain header
> tuning, but the physics is wrong. It has more to do with reflection of
> shock waves back towards the ports (and when they arrive there) than
> momentum creating suction. That's one reason why "stepped" headers are
> beneficial - they create a series of smaller spaced-out reflections,
which
> widens the power-band. Read a good book on exhausts or the book that
comes
> with a software-dyno (I forget the title).
>
> --
> Randell Jesup, Scala US R&D, Ex-Commodore-Amiga Engineer class of '94
> Randell.Jesup@scala.com
> #include <std/disclaimer>
> Exon food: <offensive words no longer censored - thank you ACLU, EFF,
etc>
>
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