Same engine with different HP. How/Why?

[Andrew_Chang@providian.com]

I know that a number of cars from Audi share the 2.8L 30v engine. Each has
a different HP, but the same torque. Is this just differences in the ECU?
Emmisions systems?

For example
US Spec A4 2.8      hp=190    torque=207
EuroSpec A4 2.8     hp=193    torque=207
US Spec A6 2.8      hp=200    torque=207
EuroSpec A6         ???

If aftermarket companies say that they have an ECU replacement that will
boost HP by "10%" is that relative to each cars' starting hp OR does the
2.8 engine have a maximum hp without degrading fuel, emmission, etc? (i.e.
if a company sells a chip for A4 & A6, then they both should have the same
final hp?)  If this was the case, then the A6 would have the smallest
increase due to chipping and the US Spec A4 the largest.

I'm not thinking of chipping at the moment. Just curious. I thought that if
the change was due to different ECU programming, that the increase in hp
would have brought about a similar change in torque too, so the 207 across
the board is what I find odd.

Don't have any engine performance knowledge to back this up, so please
educate me.

Andrew
98 A4 2.8qms