I actually wasn’t planning to upgrade the OEM Compressor Bypass Valve (CBV), but I am glad I decided to do so with this ProPerfekt piston type Diverter Valve (DV).
The rubber rings don’t leak (so much) boost, which means the power output is better (and faster) compared to the stock CBV. The stock CBV has a rubber outer ring (diaphragm) and a plastic ring on the inside (this is the flaw in the design).
The ProPerfekt DV is a known mod with the Renault Megane RS drivers, but I haven’t seen it before on another Volvo forum. The results are clear to me, the boost buildup is quicker, which means the car is faster. I would recommend this mod to anyone who has a TD04 turbo (who is still using the stock CBV). My S80 has the TD04HL-13T turbo, but will also fit the TD04HL-16T. Please note that the CBV I had fitted is quite new, so no ruptured diaphragm or something.
And this is how it compares to the stock CBV.