Valley of Death.....
Its the area between primary and secondary stages of the turbos.....
First turbo despools to match the secondary turbo, then they both come on together..... theres a nice 'kick' when you experience both turbos coming in together, under normal driving but! when your pushing a bit to overtake, the VOD is normally just at the point your going to change gear!!! = loss of boost
you then wait until it all comes back in, normally with a bit of a bang
You don't get it as fierce in the autos but it can be a pain in the manuals...