Diesels have absolutely NO use for a dump valve. The reason petrol cars have a DV is because when the throttle is closed the air hits a brick wall, builds up back pressure and stalls the turbo... The DV releases that pressure and keeps the turbo spinning. On a diesel, there is no physical throttle, therefore no brick wall. the air in a dieal ALWAYS has somewhere to go so it can really only be for the noise...If it had a use someone would have done it long before now.... They just sound daft on a diesel too.
Rich