RE: Turbo questions - K24, WG Spring etc.

["Michael Pederson" <mlped@concentric.net>]

Boost is a function of two things, engine rpm & load.  You can have an
engine turning 7,000 rpm yet making no "boost."    If you don't think so,
try parking a car with a turbo and a boost gage in your driveway and rev the
engine up to 7,000 rpm - no load, no boost.  You can even drive down a flat
stretch of road, and as long as you lightly touch the throttle you should be
able to get the engine up to redline without ever seeing any, if much boost.

Why stop with shimming the waste gate closed if that made more boost
"sooner", i.e. at lower rpm?  Why not weld it shut.  Welding or shimming the
waste gate doesn't "make" boost - all the waste gate does is allow you to
control the boost once it's already there.  It does not make boost occur at
lower rpms.  If you think about it, all a stiffer spring, or shimming does
is prevent boost that's already there, in the system from being bled off at
the waste gate.  And, if the shim or spring is set high enough, it will also
prevent the ECU from doing its job of regulating boost as well.

What are the drawbacks?  Well the wastegate wasn't put there to take the fun
out of driving the car, it's a safety device.  The final draw back with
shimming is that you may be ok till you reach the point that it, the shim,
actually interferes with or restricts the safety device's (the wastegate)
ultimate ability to bleed off excess pressure.  If that happens, and you get
too much pressure because the wastegate can't open wide enough, or quickly
enough to bleed off excess pressure, then something breaks.

On the S cars, I believe the waste gate spring is really supposed work as a
"fall back" device (I may be wrong about this), and the real work of
managing boost is supposed to be controlled by the ECU working with the
engine knock, and other sensors and the waste gate frequency valve to
pressurize the diaphragm under the spring, releasing or adding pressure to
allow boost well in excess of the "normal" springs 8 to 9 lbs (I think
that's what the springs are supposed to provide, but I'm not sure about it,
maybe someone else has actual figures for what the stock springs are
supposed to release at without ECU control.)  The spring merely sets the
'minimum" boost level, not the maximum cause its too stupid to know if you
got a bad tank of low octane gas, or if the ambient temperature is over 100
degrees etc. - i.e. conditions that contribute to detonation etc.

Mike Pederson


----Original Message-----
From: owner-quattro@audifans.com [mailto:owner-quattro@audifans.com]On
Behalf Of Swann, Benjamin R. (BSWANN)
Sent: Monday, November 22, 1999 2:54 PM
To: 'Sachelle Babbar'
Cc: 'quattro@audifans.com'
Subject: RE: Turbo questions - K24, WG Spring etc.

So I could get boost to occur at lower RPM by shimming the existing wastgate
spring?

This sounds like an inexpensive mod. worth doing.  Any caveats,
BTDT/procedures from the list.  Parts specifics from Home Depot or other?
If I could get boost to come on at a lower RPM - great!

Why get the K24 turbo then ?

Thanks for the replies.

Ben
correction - '85 4KQ - (not turbo) $1200 or will donate soon for tax
writeoff.
'86 5KCSQT
'87 5KCSQT Wagon


-----Original Message-----
From: Sachelle Babbar [mailto:sbabbar@iris.nyit.edu]
Sent: Monday, November 22, 1999 3:21 PM
To: Swann, Benjamin R. (BSWANN)
Cc: 'quattro@audifans.com'
Subject: Re: Turbo questions - K24, WG Spring etc.


I have just used a kh spring in my mc. Not compatable, but I made the
necessary parts swaps for it.

The wg spring is what gives you the boost. The wastegate valve opens
gradually as boost rises, not at it's limit. Consequently, you will have
turbine (hot side) bypass fairly early. Not necessarily good for turbo
lag. A stiffer spring ie: progressive may be light in the intial travel,
allowing for the wg valve to open early, but a limited distance. Further
boost (as rpm rises) will develop as the spring goes into its
progressively higher rate.

Power is not necessarily how much there is, it's how you get it; it's
speed of onset and location. Maybe that's why you see so many cars with
less power accelerating faster than more powerful cars. Flat torque curves
in 3B and 20v turbo 1.8's help quite a bit.

The power and toque curve is altered.

I have a valve tee'd off from the lower line of the wg to the upper to
raise boost. This effectively gives a stiffer spring asnd will change the
curve of boost.

The kh spring that I've installed has a more linear action than the mc.
The mc is very soft in the beginning, reducing low end boost due to early
exhaust bypass of the turbocharger turbine. With my wg controller, it just
stayed closed a really bad power curve;shot up too damn fast. Was unusable
and could not develop more than 1.4 bar in first gear because the engine
rpm shot up so fast. The Kh spring allows for more torque and a
m=noticably more usable, flat power curve. I'll correct myself and say
that the engine doesn't develop more torque (as I've seen), but is more
torquey and feels much faster. The power is more controllable while
driving at high boost levels (where they may vary).

On the highway, I no longer need to drop a gear to get around turbo lag or
open the wg controller for 2.0 bar. The low end is dramatically improved
and midrange is excellent.

Believe it or not, the traction during acceleration (hard) is much
improved. This is from rest and at speed.

I would suggest for mc owners who don't like this characteristic to simply
shim the wg spring and post the results. I'd do it myself, but am too lazy
and busy to go back to the old spring and back to the new one.

On the larger dia kh spring, I used this bronze colored split rings from
home depot. They're like snap rings that you need the special needlenose
tool for. The inside circumference is perfectly round as the extra
material for the holes are around the outer circumference. They have a
loose fit in the perch and are maybe .25 mm in thickness. On my old kh, To
go from 1.48 bar-1.68, I needed seven. 3 bottom, 4 top. Find the
appropriate size for the mc spring.


****************************************************************************
*Steve                                             Sachelle Babbar
*'87  5000CS Turbo 5spd 1.3-2.0 bar             <SBABBAR@IRIS.NYIT.EDU>
*Cockpit adjustable wastegate, AudiSport badge
*
*Disclaimer:"Any information contained herein is based purely on my own
*personal experience and may not necessarily reflect yours. Use caution as
*your results may vary from mine."
****************************************************************************
****





On Mon, 22 Nov 1999, Swann, Benjamin R.  (BSWANN) wrote:

>
> I guess I still have much to learn about forced air induction.
>
> With regard to the comments in previous posts about K24 turbo and various
> wastegate spring, I could probably use some re-education to straighten out
> my understanding.
>
> I can understand how the K24 turbo can create more boost at low end.  It
is
> one of the upgrades I would consider for my '87 5KQT wagon, to help get
more
> low end torque.  Currently, the boost doesn't kick in until higher revs,
and
> then it is almost too much, 'cause I'm shifting by the time it kicks in.
> Car is great on the highway though - will hit triple digits easily.
>
> BTW I have the car set to get about 1.9 bar through a pressure regulator.
I
> almost never drive the car that way , however, some test runs got over
> 2.0(22 PSI) until I backed off because I was blowing the end caps of my
IC,
> and I didn't think it would be good to do more than this on a stock
engine.
>
> How then does the wastgate spring contribute to low end boost.  I thought
> the wastegate was strictly to control overboost conditions, and has no
> bearing as to when boost starts to kick in.  But comments in the posts
> indicate one can change a spring and get more boost at low rpms.
>
> What am I missing here.  Is there a low cost way to get my current turbo
> (stock = K26?) to spool up faster?
>
> Appreciate comments/dissertation to further my understanding to make
> enlightened decisions on how to obtain better performance, esp. on the low
> end.  Hope I'm not starting any turbo wars here.
>
> I eventually would like to be able to use the wagon for towing a moderate
> load compfortably.  I feel right now it would be aggravating to get stuck
in
> stop and go traffic at the Bay bridge towing a camper or boat.  I doubt
I'll
> be hitting over 100 MPH frequently, but just curious, how is top end
> affected by K24, etc?
>
> Comments below prompted my curiosity.  I assume the KH is the KH engine?
>
> Regards,
>
> Ben Swann
>
> '85 4KQT - For sale $1200
> '86 5KCSQT
> '87 5KCSQT Wagon
>
> >The spring allows for poor bottom end.<
>
> >KH spring + MC engine. Wonderful match. There is more down low torque and
> >the power is useable. Stock, a mild in crease in boost, maybe .1-.2.
Power
> >arrives earlier, but more progressive and incredibly controllable (I have
> >a fwd 5 speed). It's overall a torquier feeling engine and I actually
have
> .what feels like power in the wg controller closed position. I've restored
> >the adjustability in the boost increase; I haven't seen 1.7 bar since my
> >old kh. Just goes straight from 1.5-1.9. I can execute many maneuvers
that
> >I haven't been able to since my kh.
>
> >Conversely, I feel that the lighter mc spring in the kh + the wastegate
> >controller would be a wonderful combination due to the engine's better
off
> .Idle torque.
>
>