OK, so what about decatting?

You can decat the car. Before that log the car with Lexia software and then after the decat log it again. If there is big difference in boost you can correct the N75 maps.

You can take a look for some maps in 3d view here:
edc15c2-3d-graphs-units-hw-0281010877-sw-1037353776-t54

RPM freak wrote:You can decat the car. Before that log the car with Lexia software and then after the decat log it again. If there is big difference in boost you can correct the N75 maps.

There will be very little difference or no difference at all.
I'm talking about back pressure limiting exhaust flow.
Let me explain.
Ideally:
You want a 1.5bar boost -> you close the wastegate -> turbo spools up
1.5bar reached? Yes -> Open wastegate at 20%.
20% is a calculated value that will allow the turbo to keep 1.5bar boost at a given rpm.
If you ask more boost, wastegate will close, and it will open when it is reached. when reached, wastegate will open at a % value that will keep desired boost stable.
What really happens
If you control the wastegate like the ideal situation you will have a lot of overboost.
This is because wastegate is a small passage and when you open it, there's still a lot of flow to the turbine and turbo will continue spooling up. so what is done to prevent this? engineers simply open the wastegate a little bit before desired boost is reached. this way you can stop the turbo from spooling at desired boost pressure. problem is how early to open it? too early opening will not get you desired boost, too late will get overboost. So it's a calibration engineers do. It depends on how large the wastegate is = how many exhaust it will allow to bypass the turbine.
Why we don't like it this way??
Because opening the wastegate earlier to prevent overboost, it will take longer to achieve desired boost.
We want things fast!
An external wastegate will allow more exhaust to bypass the turbine.
This way you can open the wastegate not too early before desired boost is reached --> reach desired boost faster!
But, we don't have external wastegates.
Of course, wastegate is calibrated in relation to what backpressure a certain car has.
Imagine an engine at constant 2000rpm. Fully open wastegate.
No backpressure -> in 5 seconds 800cc of air will flow.
Medium backpressure -> in 5 second 600cc flow.
(800cc and 600cc are invented values, it's just to understand)
If you calibrate the wastegate with no backpressure, you're expecting a certain amount of air to flow when you open it.
But if you apply backpressure in this case, LESS air will flow.
The other way is:
Engineers calibrate wastegates knowing how much backpressure the car have.
They will open the wastegate as late as possible to reach desired boost fast, but early enough to prevent overboost.
So they do this at the limit of the existing conditions.

Now, what I'm saying is:
If you remove backpressure from the system,
You can push those limits!
Because remapping the wastegate with backpressure will get you nowhere. You are at the limit.
But remapping the wastegate with no backpressure, will allow you to go to a new limit, where you open the wastegate later than before, and reach desired boost faster, but still not getting overboost!