EFI constantly monitors the A/F mixture via the exhaust gas O2 sensor and adjusts the injector duty cycle (richer or leaner charge) for optimum burn and power. It also atomizes the fuel closer to the valve to keep its surface area at its maximum burn stage. When you drag air and heavy fuel down an 8 inch sweeping runner that is not heated, your going to lose some atomization of the fuel. With EFI, the injectors are close to the valve and the intake becomes 'dry', only a conduit of light air: it could go through a maze and not hurt the process (look at some modern plastic intakes!) On cold starts, its a real delight to turn the key to on, wait 3 seconds and hit the starter without even setting a choke or touching the gas pedal. On cruise, the EFI can lean itself out to an extent and increase mileage, never running richer than needed. VW cheated and let the engines run very lean for economy on the street, but that increases NOX output. When they were in dyno roller 'test mode' (probably sensing the rear wheels ABS not moving?) , they did not allow that and therefor passed federal emissions. Sneaky Krauts!
