
Blow off valves and dump valves.
When the throttle is closed (when you lift off the accelerator) in a turbo driven engine there is a build up of pressure as forced air is still coming from the turbo. Lifting off the throttle is a lot like putting a plug in the sink – the flow through is stopped and water would just build up and overflow the sink.

Fitting a strut brace and performance benefits "Strut your funky stuff" Think of a car like a shoebox with no […]
How to avoid engine knock and pinging
So what exactly is engine knock and how dangerous is it? What causes engine knock and how can it be avoided?
You may notice a knocking or rattling noise from your engine or a sudden loss of power under full throttle.
Immediately back off the throttle and only use low rpm engine speeds until you can get the engine investigated.
The chances are that you are suffering from a condition known as “engine knock”.
How to add a turbo to a non turbo car.
The basic reason for forced induction (turbo or supercharger) is not to increase compression or the maximum pressure in an engine cylinder, it is to increase volumetric efficiency (the efficiency of the engine at drawing in air) although forced induction is the most effective method of upping compression.
In computer games we just tick a box, and within seconds our car is fully turbocharged and running much faster. In the real world things are very different.