ADJUSTABLE BOOST PRESSURE WITH ECU OVERBOOST

[rmeyer.rdi@reutech.co.za (Renier Meyer)]

I don't have a 1.8 / 2 bar WG spring from Scott Mo yet, but have been
running a pressure mod to achieve the same effect. My waste gate got
stuck and this focussed attention on the issue. I have improved the
system to allow over boost under ECU control.

PRINCIPLE OF OPERATION
As I understand and have seen from my experiments: On the 200T, the WG
is kept closed by the WG spring pushing the diaphragm down. This allows
the turbo to spool up until the pressure exceeds that applied by the WG
spring, at which time the waste gate opens and prevents the boost
pressure from increasing.

The ECU allows limited over boost by applying manifold pressure to the
top of the WG which forces the WG to stay closed and cause higher boost
levels.

ADJUSTABLE WG OPERATING PRESSURE
By applying manifold pressure through an in-line air valve directly to
the top of the WG, the boost level can be adjusted in increments of .01
bar (multi turn valve) by adjusting the valve. Most of these mods. that
I have seen however override the WGFV.

ADDING ECU OVER BOOST
To add ECU controlled over boost to such a system, you need to apply
manifold pressure as modulated by the WGFV back onto the WG. To do this
you put  a tee from the manifold before the in-line air valve (Full
pressure) and apply this to the WGFV as in the standard configuration.
Feed the return from the WGFV back to the WG input where it normally
goes by adding a Tee after the in-line air valve.

RESULT
Adjustable boost pressure controllable in fine increments (ideal for
testing new ECU Eprom values), with extra over boost for the WOT
conditions.
(Too see what difference this makes, have a look at the measurements
done by Scott Mockry. Details on his web page
http://www.teleport.com/~scottmo/waveform.html )

I have used FESTO compressed air valves capable of handling >5 bar air
pressure. They come in a multi turn version that locks in place after an
adjustment has been made. Cost +-$30 /valve. The pipes I used are normal
vacuum pipes from the Audi agents.

I have been running the basic mod for about two years now and have just
added the over boost function. To fool the ECU pressure gauge I had
another in line air valve that prevented the ECU from seeing higher than
stock boost values. I do not recommend this, as you will end up with the
ECU retarding timing at high boost levels.

Scott Mo. and a few other people can sell you remapped EPROMS for higher
boost.

DISCLAIMER
I take no responsibility for what you do with the information.

A SIMPLER MECHANICAL WAY
Replace your stock WG spring with a 1.6, 1.8 or 2 bar spring. Scott
Mo.and others can help you find them.

Hope that helps those who have been looking for info on this mod. Please
read the ABC's of running higher boost on Scott Mo.'s site before going
any further.

If you don't agree with me please let me know. Diagrams available for
those who want more information.


Regards,

Renier Meyer
89 200T Durban South Africa.
84 200