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Speedster injector test

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Sunday, 22 August, 2010

Speedster injector test

The maximum dutycycle of an injector is important. When it becomes too high, heat problems might occur but more importantly the accuracy of the fueling will diminish A usual upper limit is around 80 to 85%.

The ECU has a possibility to up the maximum dutycycle of the injectors, to keep the fueling in order. If this change isn't made, the injectors won't be able to deliver enough fuel for a tuned engine (2.4 intake + good exhaust).

To test the actual dutycycle of the injectors, we connected a scope to my car.

The scope is connected to a notebook where the software shows the information. With special clamps the scope is connected to one of the injectors.

With a low engine load, the scope shows the following picture.

With high load and high RPM's we got the results below.

According to the scope the dutycycle is around 93%. Repeating this test gave values between 90% and 93%. These values are only seen at high RPM, so the injectors aren't run very long at these dutycycles.

In the piece I wrote on injectors there is information on the relation between dutycycle, injector size and maximum power.

Based on thie information the following formula can be used:

Maximum power = SF * (D / 100) * 4 / K

Where:

  • SF == static injector flow, in this case 252cc/min
  • D == duty cycle, in this case an average of 91%
  • K == contant, this is 4.6 for NA and 5.6 for turbo and superchargers
Filling in the formula you get the following values:

Maximum power = 252 * (90 / 100) * 4 / 4.6 = 199hp