The last few drives I've been playing with the boost controller sensitivity setting. It was set to 20 (not that this means anything since it's application specific), so I tried increasing it to 30 (although I was a bit weary since this is quite a big step).
I drove to Amsterdam on Saturday evening so got a good opportunity to load up the engine on full boost on the A4, keeping a close eye on the TomTom for cameras. I noticed that sustaining full boost gave the tell tale signs of a too high sensitivity setting, since the pressure gauge needle "wobbled". Before switching off the engine when I arrived at the first port of call, I quickly checked the maximum boost attained during my journey (my boost controller records the highest achieved boost level) and noticed it was high at 1.26 bar.
On one occassion during the drive I noticed a distinct hesitation during accelleration at maximum boost. It lasted a fraction of a second and I'm pretty sure that it was the ECU cutting the fuel supply to the engine after detecting a condition that it considered a bit on the extreme side.
While driving, the boost seemed to be responding very quickly to the throttle, which was nice. However, the wobble at full boost and the pressure spike are not really sustainable if I want longevity from my engine. Therefore, I reduced the sensitivity down to 25 before my next drive. This time, I no longer observed the wobbling needle at full boost, although when I checked the maximum attained boost level at the end of the drive it was still a bit high, indicating that the car was over boosting, I think in the lower gears where the revs ramp up quickly. I've therefore trimmed a little more off the sensitivity to prevent the spike a little, down to a setting of 23.
I very much doubt that this will have an impact on my ultimate power rating from the car, but soon I will be able to get a better idea since my PLX Device R-500 data logger arrived today! I'm not exactly sure when I'll get to install it and will probably have to do so over a few weeks (after first buying a solderer... I've not done any soldering since I was at school so I'm a little anxious about tapping into the car's wiring). I'm looking forward to seeing the data though... should give quite an insight into what's happening with the car...