Re: What's this new chip/ "tuning" thing all about?

[aspeer@mail.utexas.edu (Andrew J. Speer)]

>1.   Chip upgrades.  Huh?   How do you get the A4's 1.8T engine to 170
>or whatever hp when 150 was all Audi got it to?
>
>2. I'm assuming you must give up something to get something here - fuel
>efficiency, engine life, parts life, your first born son, etc?  What's
>the catch?
>
>3. Key question in my mind:  Why wouldn't Audi tune the engine up to
>maximum performance themselves?
>

I'm definitely not the best equipped to handle this question, so my words
are far from gospel....so anybody who really knows what he is talking about
(or at least thinks he does) is welcome to flesh this out.

As far as I understand there are three principal variants in modifying an
engine's output.  These are A. air, B. fuel, and C. timing.  Turbo engines
are eminently more tweekable than normally aspirated (NA) engines because
they allow you to significantly alter all three variables, versus only the
latter two.    Most significantly they allow a modification of A.  i.e. pump
more air into each cylinder per combustion cycle.  The more air you get in,
the more fuel you can burn, which is achieved by regulating fuel injection.
With more air and more fuel you get a more powerful explosion.  A more
powerful explosion translates to more torque and thus more power.  The
average turbo can pump more air into an engine than the engine can handle.
The reason is that: A. The engine's long term life is jeopardized by the
increased violence of the explosion; B. The fuel injection system can't cope
with the excess of air and leads to an air/fuel mixture that is overly lean
for optimum combustion.  This is where modified chips step in.  
A.  On newer sytems they can control the point at which the engine decides
the turbo is providing too much air.  The threshold level at which the
"wastegate" lets go the excess air is increased, and thus higher "boost"
maintained.  On older systems, this function is fulfilled by a stiffer
spring on the wastegate.
B.  This would be of little use unless the fuel injection rate can also be
increased, a function the car's ECU controls and subject to manipulation by
"performance chips".

The reason the engine is not factory tweaked to maximum performance is a
matter of durability.  But this must be taken with the important caveat that
most people maintain their cars poorly.  Thus "chip" tuners can exploit this
margin, and the car can live a perfectly normal, long life if properly
maintained.  This is particularly true for cars, such as Audis, that are
overengineered in the durability department.

The Audi 1.8T engine in particular can make important performance gains
because it was deliberately kept less powerful than the bigger, more
prestigious, more expensive (and profitable) V6.

Andrew Speer
(A law student, not an engineer, so please take this into consideration
should the urge to char broil, grill, or otherwise torch my post come to
anyone!)