I think that I've found a little bug.

1. Get a car with turbocharged engine,
2. Accelerate to (for example) 30 mph,
3. Don't change gear to neutral,
4. Press I to set the ignition off,

And now (when ignition is off) press the gas pedal to the metal - do you hear turbo sound? I think you shouldn't... ;-)

http://img387.imageshack.us/img387/7553/lfsturboeb3.jpg

Yea man and thats not the only thing when u accelerate u can see that the fuel goes down when ignition off

That's perfectly fine, as long as the engine produces exhaust gas (even if it's just air), the turbo's turbine keeps spinning.
The pistons still compress air when you're in gear, which will then leave the cylinder through the manifold like normal exhaust gas would.

Quote from morpha :

The pistons still compress air when you're in gear, which will then leave the cylinder through the manifold like normal exhaust gas would.

Yes, they compress air but pressing the accelerator won't change anything. Since the turbo spools when you rev your car and more exhaust gas go out, but when your engine isn't running, pressing the accelerator won't make the pistons go faster/create more gas/rev the engine.

Hope you get my point.

Quote from mixer13134 :

Yes, they compress air but pressing the accelerator won't change anything. Since the turbo spools when you rev your car and more exhaust gas go out, but when your engine isn't running, pressing the accelerator won't make the pistons go faster/create more gas/rev the engine.

Hope you get my point.

But it will open the throttle valve so the compressed air from the turbo effectively feeds the turbo again instead of getting blown out the BOV / resisting the turbine

It would never spin turbo when no combustion is happening, let alone building up 1,73 bars of pressure (XRR)
(Besides, the BOV is blowing out air before it enters the engine, and not before turbine, but that is another thing.)

Turbo is not simulated right.

I stated in another post, but found the bugreport.

" The turbo-spooling simulation is not taking into account whether engine is running, it looks like it is just a RPM * THROTTLEPOSITION simulation, instead of RPM * DELIVERED TORQUE simulation (which would come a bit closer to real) "

Think a little. Turbo building pressure without fuel burning would't be a petrol-engine anymore. It's called perpetum mobile

It makes sense that boost would build until a certain point, and then steadily drop with RPM. Because, the blow off valve would be open when you aren't on throttle, and then, you run out of gas and floor it. The engine is still turning, and pumping air. It spools the turbo up once the blow off valve closes. Since you are flooring it, but no fuel is being added, it's pretty much air alone that is keeping the turbo spinning. It stays at maximum boost, wastegate is opened, but then the engine obviously is slowing down from internal friction, and the friction of the tires on the road, wind resistance, etc etc. So since the RPM is dropping, less air is flowing through the engine, and the boost drops. Until eventually the engine stops, and therefore there is no more boost.

EDIT: OH, I tested it out in LFS and I see what everyone is talking about. The boost actually increases from the point at which you cut the ignition, and when the RPM is dropping. That obviously is incorrect.