GoLowDrew

A guy last night got at GTI and you can hear the blow off valve in his turbo.

Questions.

- What is blow off valve, what does it do?
- Do all turbos have them? How about supercharger?
- What about Turbo Diesels?

ion_four

Search Function. If that fails, Google is your friend.

Flamenco-T

- What is blow off valve, what does it do?

it bleed out air as yout throttle plate closes to prevent the air from returning to the compressor blade and spins the opposite direction (compressor surge)

- Do all turbos have them? How about supercharger?

Yes, all turbo has them, you may be able to get away from need to have one on an auto, since there's are no load when the throttle plate closes. It's a good insurance for your turbo

- What about Turbo Diesels?

see above, all turbocharger system need to have one again as insurance for your turbo

stan

BROOD

Not all turbo diesels have throttle bodies though. In that case a BOV is not a good idea. (I'm talking larger engines here such as Powerstrokes, ISB, etc)
Eventhough I am not that familar with the VW turbo diesels, I imagine those have throttle bodies. A BOV could serve a function here.