[s-cars] I don't understand

[MLP]

The short answer, per Mr. Van Vugt of New Zealand, "The effect of
lowering the static compression ratio has a consequent lowering of the
expansion ratio and thermal efficiency of the engine. The expansion
ratio in a cylinder is a measure of how much compressed air/fuel mixture
in the combustion chamber can expand (and therefore exert pressure on
the piston) before the exhaust valve opens. It is the expansion of the
heated gases in the cylinder that does the work to run the engine, so
the expansion ratio has a direct bearing on the engine's performance.
The lowering of the expansion ratio in an engine is proportional to the
compression ratio. By lowering the compression ratio (increasing the
combustion chamber volume) in a supercharged motor, we can get a larger
quantity of air/fuel mixture into the cylinder, which will expand with a
proportionally greater force once it is burned. Therefore by lowering
the compression ratio and increasing boost the engine power and Mean
Effective Pressure can be proportional increased without exceeding peak
cylinder pressures. This is why it is better to run less static
compression ratio and more boost to produce more power."   Henry Van
Vugt, Automotive Components NZ Ltd from 

  http://www.repco.co.nz/services/news_details.asp?artid=172&off  

Sounds simple, I guess.  I'm still looking for a good long answer.

Mike