direct gas injection isnt very practicle in a car. the gas dosnt get time to atomize with the fuel. the general rule when it comes to injector placement is the farther away from the combustion chamber you can put the injector the more power you will make. the down side is more emmisions. the only good thing about GDI is low emisions, not more power.

as far as i know diesels and 2 stroke jet ski's are the only widely used direct injection. both are 2 stroke and need the direct injection for emisions purposes