Compression values


Jun 1, 2010
Seat leon cupra tdi, now gone.. A8 4.2TDI
Hi all, Couple of questions I am trying to find the answers for..

I have done lots of googling but unfortunately still haven't found what I was looking for.

I had a compression test done by a local garage who advised that I had low compression of 255PSI on cylinder 5, cylinder 6 also had slightly low readings at 360PSI but the rest of them all came in aroundabouts 400PSI.

So question 1.
Is the 400PSI statement correct? Is that what it should be?
Question 2.
If this cylinder was low and only producing 250, would it be enough of a reduction to reduce the turbo speed on this bank?

There isn't any hugely noticeable misfire but you can hear a bit of a deep blob blob blob from the airbox on that bank, it isn't that different to bank 1 really but just thought I'd mention it..

Car is Audi A8 with 4.2 CDSB engine which is laggy, down on power and guzzling diesel as if it's free...

VCDS logs of charge pressure and turbo speeds state .5bar of boost down against requested and turbo No.2 spinning considerably slower than turbo No.1