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[[Mk4]] Info: New "variable volume" intake on new (1999) VR6

From gti-vr6-owner@cobra.ccsi Thu Jan 14 11:22 CST 1999
From: "Christopher Morgan" <cmor@home>
To: "GTI VR6 list" <gti-vr6@cobra.ccsi>
Subject: [gti-vr6] New VR6 stuff
Date: Thu, 14 Jan 1999 12:19:20 -0500
 
So I have here in front of me the VW Service Training book for the New Golf,
Jetta, and GTI.  There's lots of neat stuff and no, I don't know how you can
get a copy of it.  I can't even get a copy of it.  The one I have is
borrowed and has to be back in a couple of hours.

To quote a topic of interest:

"The VR6 engine has a new intake manifold that increases low RPM torque and
high RPM power.  It does this by taking advantage of the self-charging or
ram effect that exists at certain RPMs.

"By 'tuning' the intake runner length, engineers can produce this ram effect
for a given RPM range.  A manifold that has two different lengths of runners
can produce the ram effect over a broader RPM range.

"The VR6 engine uses two lengths of runners but not in the same way as the
dual path manifolds used on other engines.  Instead of using high velocity
air flow in a long narrow manifold runner to ram more air into an engine at
low RPM and then opening a short large diameter runner for high RPM, the VR6
engine takes advantage of the pressure wave created by the pressure
differential that exists between the combustion chamber and the intake
manifold.

"All air enters the intake manifold plenum, referred to as the Torque Port
and is drawn down the long intake runners to the cylinders.  A second plenum
called the Performance Port, which is attached to a set of short manifold
runners, joins the long intake runners near the cylinder head.  A Rotary
Valve separates the Performance Port from the short runners.

"Note that the Performance Port does not have any other passages to the
intake manifold other than through the Rotary Valve.  It does not have
access to the Torque Port and does not admit any more air into the cylinders
than what is already drawn down the long intake runners."

There are a few more pages with illustrations and a more detailed
description of how the pressure wave stuff works (Physics 122).  The
interesting thing is how the two plenums work.  One is at the end of a long
set of intake runners and is called the Torque Port.  It is also connected
to the throttle body (which lets air in of course).  The second plenum,
called the Performance Port, is attached to a set of short runners and has
no other connections to let air in or out.  It is basically an empty chamber
that lets a pressure wave bounce around and exit out the same runners from
where it entered.  The Performance Port is closed off to the rest of the
intake tract between 900 and 4300 RPM by the Rotary Valve, which is a long
cylinder with six holes cut through it perpendicular to its axis.  The
Rotary Valve rotates 1/4 turn to open or close and is operated by a vacuum
solenoid and change-over valve that in turn is regulated by the ECM.  If you
look here http://home9.swipnet.se/~w-90969/vr6_4v.jpg (this isn't the same
engine that is shown in the book, but you'll get the general idea) you can
see the bulge across the front of the intake manifold that houses the Rotary
Valve.  Seems pretty cool to me, and apparently it works.

Other things mentioned are a dual mass flywheel, an electronic throttle, and
the new Bosch ME7 Motronic system.  The first item reduces NVH in general
and gear clatter when idling in neutral.  As for the electronic throttle, it
also reduces NVH transmissions and allow the ECM to pick the optimum
throttle setting (regardless of what your right foot may be saying).  I've
driven a few TDIs that also have the drive-by-wire set-up, and I'm not
exactly sold on it.  The pedal feels dead.  I prefer the direct feedback
that a cable gives.  As a side note, because the ECM can now control the
full range of the throttle, the functioning of the cruise control was
integrated into it.  Thus, there are no more vacuum lines, pump, and servo
like on the A3.  The ME7 system if left to a separate training manual that I
haven't seen yet.  It may not even be out yet.

That's all for now, gotta go.

-Chris



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