Re: chips and HP and turbos

[orin@netcom.com (Orin Eman)]

> some more details from the excited claimants would
> certainly be appreciated.  How, exactly DOES a chip
> affect a wastegate, for example?

Well, I have already done this kind of mod on my 86 5k CSQ.
The way the wastegate works on this car is as follows:

The wastegate is activated with a pneumatic actuator using boost
pressure.  A spring holds it closed.  The more boost, the more
pressure agaist the spring.  Eventually the boost pressure
overcomes the spring and the wastegate opens.  On the Audi actuator,
it is also possible to add pressure on the opposite side of the
actuator.  This adds to the force provided by the spring and
delays the opening of the wastegate.  On the 5kCSQ, the
computer regulates the pressure on top of the wastegate
by using a solenoid which switches between boost pressure and
vacuum from the turbo inlet.  Increasing the duty cycle of
this solenoid adds more pressure on the top of the wastegate
and gives more boost.

On the later cars, the computer regulates boost by stopping
boost from getting to the wastegate when it wants increased
boost and letting it thru when it thinks there is enough boost.

In both cases, if there is no current to the solenoid, the
boost is controlled by the spring in the wastegate.

I don't know exactly how the 1.8T computer is regulating boost, but to
get a flat torque curve from 1750 to 4600 RPM, I'll bet its
backing the boost off significantly at higher RPMs.

Orin.