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Injector duty cycle

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What is a good upper limit of duty cycle to use for an injectors?

I have seen figures of 80 and 90%

Is 80% a sensible upper limit or would people consider an absolute maximum?


80 - 85 % as a healthy maximum. If I would be in the situation of running 90% often, I would opt for increasing the fuel pressure slightly to keep the max DC at 85. Having said that, increasing the fuel pressure may not yield the desired result since flow and pressure behavior on AF are somewhat unpredictable, meaning if the electric pump is near it's limit, increasing the pressure may not further increase flow.

85% is my typical line in the sand, however the modern EV14 based injectors seem to be able to tolerate higher constant duty cycles with no ill effect. Even in this case I suggest keeping the max duty below 90%. It's always nice to have a little headroom available in your injectors.

I've had trouble with the older EV1 style of injector becoming erratic in their operation if you pushed them beyond 90% (that and the fact they aren't particularly linear in their flow up there!).

Thanks one and all....75-80% it is based on the guesstimate of what the engine may make.

Also with the injector duty cycle if you don't mind me jumping on the subject, how does the master trim milli seconds work in with the milli second amount in the fuel table? Can you explain that a little bit please andre?

What ECU brand and type are you specifically referring to?

The master trim may be regarded as an overall fuel calibration value, from what I gather. Apologies, I know your question was directed to Andre.

That's fine! that's the beauty of a forum as everyone can help where possible :)

I was referring to a link g4 ecu as in the worked examples of the practical dyno tuning course andre sets the master milli second figure then adjusts it later.. just wondering how that stacks with the millisecond numbers in the fuel table

The master injector pulse width could be though of as a coarse/overall scaler for the main fuel table. It needs to be selected based on the size of injectors and the engine's fuel requirements in order to get good resolution in the fuel table.

If we have a master pulse width of 6 ms, then a number of 100% at 100 kPa in the fuel table will result in a pulse width of 6 ms being delivered to the injectors (before compensations being applied).

Check a webinar we ran on the topic here: https://www.hpacademy.com/previous-webinars/fuel-table-resolution/

Ahh.. makes complete sense and thank you for clarifying! Will watch the webinar for more information aswell.. cheers!

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