from wikipedia ---
"A
turbo timer is a device designed to keep an
automotive engine running for a pre-specified period of time in order to automatically execute the cool-down period required to prevent premature turbo wear and failure. After a period of driving when a
turbocharger has been working hard, it is important to let the engine run at idle speed for a period of time, allowing the
compressor assembly to cool from the lower
gas temperatures in both the
exhaust and intake tracts. At the same time the
lubricating oil from the
engine is able to circulate properly so the turbine won't burn the
lubricating oil that would otherwise be trapped within the charger with the turbine rotating at high speed. With regard to modern automotive turbochargers, the need for a turbo timer can be eliminated by simply ensuring the car does not produce any 'boost' (during driving) for several minutes prior to the ignition being shut off.
Turbo timers also have the added benefit of allowing the operator to adjust the engine
RPM's that the turbo begins producing boost.
Most turbo timers are based on digital electronics."
price range of turbo timers -- 2k up