I wanted to post up some results from an engine brake mod I tested out today. What I did was increase the VNT control maps at 0 injection quantity from 2400 to 4800 rpms. I believe I set them to around 61%(6100), which is kinda low but wanted to ensure I did not overspin the turbo. What this does is partially close the nozzles in the turbine side so that more back pressure is created in the exhaust and it puts drag on the engine helping to slow it down.
The chart below shows me starting in 5th gear at ~70-72 mph and 0% throttle. I then hit the OD off button to force the transmission into 3rd, still at 0% throttle, and let to rpms jump to 2600-2700 rpm. In the chart is the RPM and boost levels from both my base tune and Engine Brake tune. I did offset the engine brake tune slightly so that they were showing the same RPM at the same time.

so the Engine brake tune shows a clear difference in boost once the transmission is shifted to 3rd and the engine is above 2400 rpm, which means that backpressure is higher and the turbo is working harder. Where I live the ambient pressure is about 800 mbar, so the stock tune was making about 140mbar of boost and the engine brake tune was making 700 mbar of boost. I show a section of 5th gear(low RPM) to show that the engine braking does only occur at 2400 rpm and above. You can see that before the downshift the two tunes are generating the same boost. So basically, this should provide an increase in engine braking
Oddly enough, the rpms seem to drop faster on the base tune. I dont know exactly why this is but it could have been as simple as the wind blowing or being on a slightly shallower angle. Ill play with this more when I get some time.