I5 Head Porting and Polish

[DeWitt Harrison]

You've asked a lot of good questions I can't answer.
The answers would have to do with whether or not,
during the course of pressure wave propagation in
the exhaust manifold, there were backward or upstream
traveling waves present. Apparently this is common
in NA engines at points in the exhaust where pipes join
or diameters change. It certainly seems to me that's it's
possible an exhaust pulse could bounce off the turbo
back toward the exhaust valve but I don't really know.
If there were backward pressure waves in the turbo EM,
then anti-reversion measures would be useful.

DeWitt Harrison
88 5kcstq

----- Original Message -----
From: "james accordino" <ssgacc at yahoo.com>
To: "DeWitt Harrison" <six-rs at home.com>
Cc: "audi list" <quattro at audifans.com>
Sent: Saturday, November 10, 2001 7:32 AM
Subject: Re: I5 Head Porting and Polish


> Is this specific to turbo engines?  I'm speaking about
> "flow reversion".  I seem to remember that the exhaust
> gases exited in pulses and the key was to interleave
> the pulses at the primary-secondary collection point
> and also at the secondary-main exhaust collection
> point.  Almost creates a suction.  This was why
> primary and secondary dia. and lengths were so
> important.  Also location and size of any crossover
> pipe.  Again I'm not sure how the turbo effects this,
> as I've got zero experience with custom exhausts on a
> turbo motor.
>
> Jim Accordino
>
> --- DeWitt Harrison <six-rs at home.com> wrote:
> > On Fri, 9 Nov 2001 06:52:29 -0800 (PST),
> >    james accordino <ssgacc at yahoo.com> wrote:
> >
> > > IMHE the biggest gains to be had occur when you
> > match
> > > the ports.  Port matching refers to equalizing the
> > > size of the port exits to the gasket.  When you
> > match
> > > both manifolds and the head ports(usually to the
> > > gasket as this makes a convenient pattern) you
> > > eliminate any ridges or lips that would disturb or
> > > restrict airflow.  [ ... ]
> >
> > Much of the porting literature I've seen recommends
> > a precise match only on the intake side. The ports
> > in the exhaust manifold are often larger than their
> > mates in the head in order to create anti-flow
> > reversion
> > steps. One good reference off the top of my head is
> > "Practical Gas Flow" by John Dalton, ISBN 1 899870
> > 08 3.
> > This is an easy to read paperback which, in addition
> > to
> > much illuminating discussion about flow in heads,
> > shows
> > you how to make a dirt cheap flow bench from garage
> > junk which gives highly reproducible results.
> >
> > DeWitt Harrison
> > 88 5kcstq
> >
> >
>
>
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