Cartridge KP39 54399880065 54399710089 BMW 335d M57D30TU2

Should I put a blow off valve on my turbo system?

Yes, a blow off valve (BOV) is a very good idea. It will keep the turbocharger alive much longer. When you are driving your car, the throttle plates are constantly being opened and closed. When the throttle plate is closed the turbo is blowing into a wall. This causes extreme axial load on the bearings, which will make the turbo prematurely fail. The BOV also keeps the turbo spinning while you shift from gear to gear keeping the spool-up time down between shifts.