Bob,
Intercoolers are a big help for turbochargers the desired effect of the
"pump" is to boost manifold pressure. Superchargers this with a pump
that takes horsepower from the engine to pump the air, turbocharges use
"waste" gas pressure, that expanding gas left after the exhaust valve
opens to power the turbine and drive the pump, therefore the power for
the pump is "free" of sorts. 
The downside is that the hot exhaust gases running from 1300 to 1600 deg
F are running through the turbine, much of this heat is transfered from
the turbine (turbo) housing and shaft to the pump shaft to the air being
compressed, therefore heating it up considerably. Heating air makes it
considerbly less dense. 
So we started off putting the turbo-charger on the engine because we
have a low-pressure problem (low manifold press) we want to increase
with the pump to get more air in the cylinder, so the turbine driven
pump doe this well, but heats the air thereby making it -less- dense and
negating some of the compressing of the pump. Therefore: Voila:
Intercoolers, they are nothing more that an intake air manifold
radiator. They are designed to cool this now compressed air to increase
the pressure again by making it more dense. Sorry for long explain but
wanted to be thorough. These are very desirable and finally they can be
rather large under the hood.
Mark B. Magee
87GL 83k
Kemah TX USA