You aren't really reading my posts as I posted what engine you have hours before you responded, about 8 hours actually. I said you have an ISL and I told you about the Cummins C brake that is a combo of compression release and exhaust braking and that is why you get boost. Cummins uses it on the ISL's to increase retarding hp.
A compression release brake without aid from a VGT won't build boost, or at least it shouldn't.
If you have enough turbine restriction to build boost (and a lot of it) freewheeling at rated rpm there is too much turbine restriction and your drive pressure while actually burning fuel would be epic. This boost wouldn't be a function of the compression release brake thou, and rather an undersized turbine for emissions reasons and the boost would be present brake on or off.
You also missed my question of how much boost are you building at 2000 rpms and the brake off? Both in N and decelerating.
So if you truly took a nice pull maybe you should have taken a reading pill too.
