Well my friend. The answer to your question is two fold .
1) Safety. By law you are allowed to increase power by no more than 20%. It does not matter whether you achieve this by tuning the existing engine, og by swapping it for a more powerful one.
Sorry Krede, I have to comment this.
Actually in DK, if you have a pre 1983 car (emissions), you can tune the engine as much as you like as long as you use the original head.
You can install a turbo, compressor or NOX, but you can not use eg. a ROC 16V head.
As I know, the 2,2 turbo head is identical to the standard one - this can be used.
If you install a new powerplant, 142 HP (170 for the S) is the limit.
Exceeding this limit requires approval form the manufacturer - or comprehensive testing by the authorities.
Politecnic used to have a traditional tune set with cam and Webers claiming 184 HP.