Quote:
Originally Posted by vstech
I like to think of it like this:
boost is pressure that the motor is blocking from flowing through the system.
at idle, the pistons are spinning freely, and there is nothing pushing against them.
under load, the pistons are pushing against the weight of the car and actually working, so the turbo needs to push harder and harder to keep the car moving.
this is an oversimplification, but it gets the point across of why no boost is present in park.
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I like to think of it like this:
The turbo requires a certain speed to produce boost. At low exhaust volume, the turbo will spin about 30K rpm.........which is not sufficient to produce any significant airflow to the engine to pressurize it.
As more exhaust gas is produced..........under greater engine load.........the turbo spins faster.........above 50K.........and starts to produce enough airflow to slightly pressurize the manifold.
Finally, at maximum exhaust velocity at high engine loading, the turbo can reach full speed..........about 120K........and push a significant amount of air to the manifold.........thereby pressurizing the manifold to more than 15 psi. The wastegate opens at this point and limits the manifold pressure to 15 psi.
In summary, you will never get any boost when the engine is in neutral..........insignificant exhaust volume and velocity to spin the turbo at high speed.