Anti-turbo lag systems

[MaxBoost at aol.com]

Not strictly DIY_EFI but sorta related.  This thread on the Saab APC system
has got me thinking.  I have seen several references in Racecar Engineering
to anti-lag systems used on current FIA rally cars like the ford, subaru and
mitsubishi.  In particular I was wondering how the system worked?

I know that early eighties ferrari F1 cars used a system that bypassed air
from the turbo compressor straight into the exhaust system when the throttle
was closed and ran a rich mixture to create combustion in the exhaust.  I
also read somewhere that peugeot used to inject propane into the exhaust to
acheive the same effect before it was banned in the group B rally cars.

Depending on how these current systems work, I would like to adapt it to my
current project.

Any info would be appreciated.

Max