My personal experience with a BOV on a TD is not a good one.
On my TD Vanagon I was running with the wastegate adjusted for boost above the BOV threshold (about 9-10 lb IIRC). Under normal around town circumstances it wasn't a problem, but when climbing a hill and really running it hard, the boost would overcome the BOV and I could hear pressurized air exiting the manifold through the BOV (the loud whoosh all you kids are after
).
It would do this in bursts if you held the pedal down. EGT's skyrocketed.
In a gasoline engine this is no big deal, a rich mixture never blew anybody's gasser up, diesel on the other hand :roll:
I theorize that as the pressure was being released, copious amounts of fuel were still be injected, the turbo was still making boost & demanding fuel from the injection pump, but the air wasn't present in the combustion chamber because it was bleeding off, which severely richened the mixture.
After that trial, I nixed the BOV and relied singly on the wastegate to regulate boost pressure. I based my settings on maximum attainable EGT of 1300 on a WOT lug run to the top of this huge hill by my house.
All one really needs for safe functionality is a boost controller valve, a boost guage and a wastegate.