First a little explanation on engine basics and air pressure.
1)An internal combustion engine is nothing more than an air pump.
2)An internal combustion engine always uses up its air supply before its fuel supply.
3)The more air you can get in and the faster you can get it out the more power you create by using more of your available fuel.
4)This is why newer cars with
DOHC Multivalve engines create much more power while getting better fuel economy, they breath much better and fuel control is much more precise so nothing is wasted.
Air Pressure
1)High pressure always moves to low pressure in an attempt to equalize.
2)The engine creates low pressure(vacuum, lower than atmospheric).
When the throttle is opened outside air(atmospheric pressure)rushes in to attempt to fill the void of lower pressure.
(Vacuum , below atmospheric is measured in Inches Of Mercury.."
HG)
(Pressure, above atmospheric is measures in Boost, Pounds Per Square Inch..
PSI)
3)The amount of air that enters the engine depends on engine size/design/age/wear on engine components and actual atmospheric conditions.
Again on ALL engines the air supply will be depleted before the fuel supply.
4)Turbochargers and Superchargers increase the atmospheric pressure in the Intake Manifold so when the intake valve opens More air than just atmospheric rushes into the cylinder.
5)As boost increases(more available air and increased temps)you have to be sure you are also supplying fuel and keeping combustion chamber temps down or you will go lean(not enough fuel) and either melt pistons or destory pistons from detonation(another topic)
6)On a normally stock engine the engine controller can read up to 2 Bar or 14.5 Lbs of boost(14.5
PSI of atmospheric pressure) and add fuel needed to that point.
Above that the controller can no longer read
Map voltage and add fuel so the controller goes into overboost shutdown to prevent lean conditions and engine damage.
Ironic though, overboost shutdown is violent and will blow head gaskets and break piston ring lands so both...lean and shutdown want to be avoided.
7)Boost levels are controlled by the controller opening the wastegate to allow exhaust gases to exit without turning the turbine side of the turbo.
8)Boost levels are set lower on a non-intercooled car beacuse combustion chamber temps will be higher and may cause detonation.
The Wastegate
The wastegate is normally closed and is opened by + pressure(boost).
When the wastegate is closed exhaust gases are routed thru the turbine side of the turbo, as the engine rpm increases and exhaust flow speed/volume increase the turbine turns faster which turns the compressor side of the turbo faster.
The faster it turns the more air is compressed and the pressure increases and more air enters the engine allowing more fuel to be used thus creating more power.
Hopefully this explanation helped cleared things up and did not create more confusion.
Any questions Please ask and remember, my PM box is always open if you want to ask out of the public eye.
If you would like to see pics of the different turbo's and wastegates go to...
Donavans Dodge Garage and click on Turbo Database.
Donovan's Dodge Garage
TurboDodge.com 
