injector question (duty cycle)

[richard cash]

when on full boost my injectors read around 70-75% of the duty cycle. What is the maximum injectors can safely go up to. Id have thought there must be a limit and they shouldnt be mapped to 100% as it leaves no room for error then.

[bnaellis]

when on full boost my injectors read around 70-75% of the duty cycle. What is the maximum injectors can safely go up to. Id have thought there must be a limit and they shouldnt be mapped to 100% as it leaves no room for error then.

I run mine up to 95% others probably wouldn\'t recommend it but then you spend so little time at peak duty cycle I don\'t really think it matters.
The general what most people adhere to is about 80-85% max.

[gsb876]

I would not worry about it unless you are getting close to 90% duty reading, when you start to mod the car to higher power a better fuel pump and bigger injectors will be a good place to start.

At 75% all is well at the mo

[Ricco_04]

I was advised by one of the specialists not to go above 85%

[Prof]

As I understand it, most injectos become nonlinear above 85%.  An explanation - Assume 800cc injector with duty cycle of 10% gives you x fuel, then at 20% you would get 2x and so on, but above 85% the amount delivered will no longer follow the rule.
 
Another way to squeeze a little more is to up the fuel pressure (assuming fuel pump can handle demand), which means for a given duty cycle more fuel will be squirted.

[richard cash]

you say its none linear but dont describe the type of curve that it produced if plotted. I.e whether it will become richer or leaner

[Prof]

- that\'s cos I don\'t rightly know.
 
I am guessing if you plotted this it would be a staight horizontal line for the first few percent, then a straight line at an angle on the graph, followed by a vertical line, as the injector would effectively be held open. So at very high duty cycle it would run rich.
 
It makes sense if you think about the injector internals. At very low duty cycle and very high duty cycle, the solenoid will not really have time to move against the spring, so may not alter the fuel flow at all. In other words for very low duty cycle the injector might effectively stay closed, so until maybe 4 or 5% no fuel will flow, then at the top end it will stick open - say perhaps 95 to 100% will effectively be fully open.
 
You should also couple this with the fact that if the injectors are open, then fuel pressure is being released off the fuel line, and the pump must supply fuel at a faster rate than the injectors use it, or else they will effectively run lean at the higher duty cycles due to fuel starvation.
 
It seems 80-85% is a good figure to work for a maximum, and still give yourself a safety margin.

[Andy_k]

As long as your not near to running lean or at 85%+ injector duty around your peak torque you should be fine. Injectors tend to stick, so i have heard if held open for long periods.

I was running up to 100% injector duty for a good couple on months and all was well, wouldn\'t recommend it tho.

In an ideal world i\'d not let them go above 85%.

[Shyne]

So many conflicting opinions and factors, if you map the car yourself you\'ll pay more attention to the affects, although it if you map the car yourself you\'ll also know why you run higher inj duties than others.

If you\'re having others tune the car and they set safe targets for you, just roll with them as they set the figures in the first place. 8o)