A very interesting thread. But what's the purpose of the turbocharger? How exactly, and to what extent, does extra torque make the game "more fun"?  

I measure the current power output of the engine and use this to calculate a "target pressure" value. A "current pressure" value then moves towards that target pressure over time (creating the delay), but is capped at a maximum. When pressure leaves the system, I store that in a "blowoff" variable that's only sent to the audio system

The torque output from the engine to the transmission is then simply boosted by a percentage relative to the current pressure value.

4 hours ago, LorenzoGatti said:

But what's the purpose of the turbocharger? How exactly, and to what extent, does extra torque make the game "more fun"?  

If you're going for a sim, it helps reproduce the "feeling" of some real cars. If you're just going for fun, the slight delay in max engine output after giving the "go fast now" user input can be a fun thing to play with.