When your engines running a turbo charger, whether its on a petrol or diesel engine, running at boost will cause a lot of heat build up. As the heat builds up, the turbo fans and housing will expand and when you have finished driving and turn the engine off, the turbo will stop spinning and parts will contract again. You run the risk of ceasing the turbo and costing you a lot of money for replacement.
Turbo Timers are the best way to let your turbo cool down before the engine is shut off, basically what they do is allow your engine to continue running for a period of time after you have turned the key. This allows the turbo to continue spinning until it cools down to a much better temperature, therefore radically reducing the risk of seizure.
The most popular manufacturers of turbo timers are;