If you don't have an electronic MAPsensor on the air inlet tube of the engine,
and you still want to boost the turbo to get the right mix of air and fuel.
Then use a bleed-valve.
This valve bleeds out a small percentage of the air pressure between the turbo and the pressure gauge of the cars ECU.
The ECU will now measure a lower barometric pressure and in order to compensate the loss of pressure it will direct the turbo to work harder to get the right pressure.
With the higher air pressure you can insert more fuel into the engine by using the power-box.
By inserting only more fuel in the engine by using the power-box,
the balance of air end fuel is not quit good.
It will lead to a to high UGT and fumagine.
On this picture below you can see some bleed-valves.
This bleed-valve below is placed into an Audi A4 from the year 1997 (motor type AHU).
The (nylon) tube from the air inlet to the ECU has to be cut in two, so that the bleed-valve can be placed in between.
Don't let to much air escape! Otherwise the turbo will be overloaded.
If you want to be safe, then you can place a turbo pressure gauge.
Now you can see how much pressure the turbocharger will give.
All risks are for your own account. If you don't know what your doing, don't even start!