Some FK2Rs have problems with the boost over 1.6 bar between 3000 and 4500rpm.
The boost is waving because the bypass valve is opening and closing all the time, ignition does the harlem shake as well. The reason for that is not the bypass valve itself, but the t-valve.
As we could see on the FK8, this valve doesn’t exist anymore
After changing many other parts without any positive results, we finally deleted the T-Valve and car ran over 1 second faster with full boost and ignition. Not every FK2R has this problem, but it’s only a matter of time this valve breaks, even it is tuned or not. This Mod is very easy to do, you have to connect the two hoses as shown on the pictures an close the intake.