Quote:
Originally Posted by SVTSHC
It is but it isn't. Think about it like this, in stock form direct injection is king with forced induction applications; largely because you don't have to use additional fuel to prevent detonation because the mixture happens in the combustion chamber and not before the intake valve thus allowing for a cooler mixture and increased volumetric efficiency.
This becomes a problem though when you're looking to turn it up a notch. The injectors atomize almost to the same extent diesels do; because your mixture happens inside the combustion chamber you end up with a limited time frame to form a homogeneous mixture. The only way to combat things going south is to restrict airflow, hence the reason he said there's a restriction in fueling because naturally if airflow is being restricted then so is the amount of fuel for stoichiometric purposes.
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My car is currently running 21 lbs of boost (instead of the stock 14 lbs) and there are no issues at all with keeping the air/fuel ratio in check. The GDI system is more than capable of adjusting fuel delivery & timing at increased boost levels.
You have to keep in mind that GDI has different combustion modes. For light loads, an ultra-lean burn mode is used. This is a stratified charge. The timing of the fuel being injected is adjusted towards the end of the compression stroke.
For normal loads, the GDI runs in stoichiometric mode. The fuel is injected earlier (during the intake stroke) and the result is a very homogeneous fuel charge.
For high loads (such as full throttle & full boost on a turbocharged car), the GDI goes into full power mode. It dumps in more fuel and creates a richer mixture to prevent engine knock.