If I remeber correctly, each pound of boost adds something like 0.3 points to the effective compression ratio.
So if you start with say 7.0:1 (stock 930) and boost it 1.0 bar you end up with an effective comression ratio of 11.2:1 which is at the limit given the combustion technology of the 930 engine.
This may seem a bit simplistic, that the relationship is liear, but I would use that mathmatical logic if building an engine myself.
Corky Bell goes into this very well in his book Maximum Boost.
RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8