RE: wg spring in mc turbo

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

I think that it was Scott J that earlier posted a bit of a description about
the way the wastegate control was effected on the MC engine.  Let me
reiterate ...

The wastegate system on the MC engine was designed for the stock spring to
be supplemented by additional boost applied to the upper chamber of the WG
via the WGFV.  The WGFV switches this port between manifold pressure and the
closest thing to vacuum you can get in the engine (i.e. a take off right at
the inlet to the compressor).  The WG spring is there to keep the WG closed
long enough for the boost to pick up and force the WG closed with the
stiffer [boost] spring.  

While there isn't necessarily anything wrong with putting a stiffer spring
into the WG on an MC engine, there is one caveat to be aware of.  The way
the system is designed, the ECU can attempt to reduce the boost using the
WGFV if it detects knock when the timing is backed all the way down.  The
benefit of the stiffer spring is that short bit of extra force when the
turbo is spinning up, which will give a little bit better lag performance,
but I wonder if anyone has actually quantified the difference.  

In my mind the preferred solution for the MC engine is to install a chip
that allows the WGFV to hold boost on the wastegate longer to allow the
higher boost (AKA QLCC).  Perhaps building something like Javad suggested
(more about that below) could allow you to stiffen up the stock spring just
a bit to allow the spring to hld the WG closed a little bit harder at first.
Anyone with an MC engine should be advised to look through the tests that
Scott Mockry lists on his website: 

	http://www.sjmautotechnik.com/boost.html 

Those of us who own ur-quattros know that Audi provided an adjustable perch
in the stock wastegate ... they just covered the adjustment mechanism with a
plug.  I'm pretty sure that the WG cap for the MC is the exact same part,
but the spring perch is held in place by an attachment from inside.  I've
always thought that it should be afairly simple matter to convert the MC WG
into an adjustable one by removing the bolt that is currently holding the
perch in place and then installing some sort of a stop in the hole in the
center of the perch (tap the hole and insert a small plug).  Now a bolt can
be installed through the cap from the outside, which would press against the
stop and allow the perch to be adjusted.  If someone saw how the adjustable
perch on the QTC worked they'd know exactly what I'm thinking about because
that is pretty much what is done there ...

HTH!
Steve Buchholz
San Jose, CA (USA)