Help w/ Turbo timing Question?

OK,

I have all the basic knowledge of how the turbo system works, and how to incorperate it with my early Z..

BUT!!!

One Part I just dont quite get......... "Timing".

stock 76' is 8 deg. (+/- 2 )..... 81'-82' turbo 20 deg... and 83' is 24 deg.

1) Why would you Advance the timing on a turbo system???

2) Can someone help me understand why with a system that you dont want detonation!!, would you have the spark start sooner??

3) Is there something about the increased cylinder pressures that slows combustion??? or do I have something wrong in my thinking this out??

Any help appreciated,

aZcarbum