When you've installed your modified APC, you'll need to calibrate it.
Remember, that any testing, tuning, racing belongs on the track and not on a public road.

BTW, have you read the disclaimer? (about->disclaimer) 

One thing that you should build/buy is a long APC cable.


This cable makes it possible to calibrate the APC without the stop 'n' go penalty.
Just plug in the cable between the APC and the ordinary contact. Then put the APC on the passenger seat and start the tuning process.

If you don't have a cable like this you'll have to stop the car, turn off the engine, dismantle the APC box, open it, do the changes and put it all back.
Then do the test-drive with the new setting. If it wasn't right, stop the car. Do this until you're satisfied.

Well, you can see that this takes time.

The tuning process (the mystery of the P and F)
On the APC there's three pot, s P,F and K.

The function:
P: Boost rise rate
F: Boost pressure
K: Knock threshold (NEVER EVEN THINK TO TOUCH THIS ONE!) 

F sets the maximum boost and this one is not especially sensitive. P controls how fast the Boost pressure rises to the F-level. If P is set too low the Boost "crawls" up, set too high the boost will overshoot the F-level, and you will experience some real nasty boost spikes until it sets or until the APC lowers the boost due to knock. The worst-case scenario, the head gasket blows.
Look below and you'll see what I'm talking about.

And now to the process.

Start by reducing the P-pot
Then set the F-pot at your desired level. 
Now the really fine work is beginning. The P-pot is very sensitive. Just start low and work yourself up until the setting is right. 

It's a lot of touch 'n' feel here. 

Measuring power
I'm using an AP22 from Race-Technology

This little beauty can measure a lot of things. 0-100 km/h, 0-Xm (you select), Quarter mile, power, and a lot more. And you can plug it to your PC and save the results.

I'll put up some measurements later on...