MJB Motorsport

2.0T FSI Fuel System Testing

The following information is derived from the Bosch Gasoline Engine Management manual...

Compared with manifold injection, gasoline direct injection differs mainly in its higher fuel pressure and the far shorter time which is available for directly injecting the fuel into the combustion chamber.

The figure below underlines the technical demands made on the fuel injector. With manifold injection, two revolutions of the crankshaft are available for injecting the fuel into the manifold. At an engine speed of 6000rpm, this corresponds to 20ms.

In the case of gasoline direct injection though, considerably less time must suffice. During homogeneous operation, the fuel must be injected in the induction stroke. In other words, only half the crankshaft rotation is available for the injection process. Referred to the same engine speed as with manifold injection (6000rpm), this corresponds to an injection duration of only 5ms.

To put this into laymans terms, the fuel injectors for FSI vehicles have a certain window of time to inject the necessary amount of fuel into the cylinder. As performance demands are raised, more fuel must be injected and the fuel injectors begin to evidence longer and longer durations to get that fuel injected into the cylinder. Bosch recommends the optimum window of time to get that fuel injected is within 5ms.

As can be seen on the below graph, APR has performed an upgrade allowing better fueling for aggressively modified B7 A4 FSI cars. The below graph depicts a 2006 Audi A4 with Carbonio intake, full Neuspeed turbo-back exhaust, and Milltek 200cpsi high flow catalytic converter. APR does not currently market a high flow catatlytic converter for this platform but recognized persons will be adding such modifications and developed a fuel solution for this. Notice that the new Stage 2 Plus program is running a small amount more boost than the standard program but is able to retain lower injection on-times much closer to the level Bosch specifies as optimal.

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