Oracle said:The chips dont alter the turbo boost, on turbo diesels, the boost is around 18psi anyway. This is preset via the wastgate, so unless the chip can unscrew the regulator and adjust it then it can only alter the fuel coming into the engine!
The VAG TDI's do. The turbo pressure is regulated by an electronically controlled valve.
What you state is true for the old skool engines like the PSA XUD. Then again these can't be chipped - hence the infamous screw mod.