P3 T6 "Kompact EM" Compressor Bypass Valve CBV eCRV

You can think of the turbocharger in a car as an air pump, physically squeezing more air (and therefore more air/fuel mix) in to the engine to make more power. Lifting off the gas snaps the throttle shut, and the turbo's pressurized air builds up behind it in the air pipes until the backpressure pushing on the turbo's compressor wheel blades stops it. This "compressor stall" means the turbo has to spin all the way up again, and is also bad for the turbo's health in the long run.

Early turbocharged cars used Blow-Off Valves to vent this excess, closed-throttle boost straight to the surrounding air, but modern turbos instead use Diverter Valves to send it back in to the air intake. You don't get the cool pshhhhhh noise of a classic rally car's BOV, but a DV recirculating that pressurized air in to the turbo inlet helps to keep the turbo spinning and allows the engine to quickly recover when you get back on the gas.

On Volvos, DVs are called Compressor Bypass Valves (CBVs) or Compressor Recirculation Valves (CRVs). The "short six" turbocharged inline six in P3 cars switched from a rubber diaphragm valve in the earlier T5 cars to a solenoid-actuated piston valve, made by electronic control system expert Pierburg. This style of CRV is pretty durable, but problems with the piston sticking, seals breaking down, or the solenoid failing are still possible...and Volvo only sells complete turbocharger assemblies, with no separately-available CRV.

Turbosmart, a quality manufacturer of turbocharger control systems and components, has come to the rescue. This CRV features heavy duty seals and pistons and a rapid-cycling solenoid in an anodized, billet aluminum body. "Kompact" here refers to its size closely matching the factory piece, facilitating drop-in, no-mods-needed installation. If you've eliminated boost leaks but still have slow or sloppy boost buildup and eCRV error codes, this is the perfect fix to get your T6 moving again.