This image is needed for the injectoropening.
Unfortunately it still does not show up in the manual.
[[Manual: Detailed.Output.Fuel.Config]]
Basic req_fuel calculation
Assume
- fuel density=0.755 g/cc
- AFR=14.7 at stoich
- intake air density = 0.0012 g/cc (at MAP=100 kPa, which might be a cheat from the real 101..104kPa ?)
- (alternate+1)*divider = N (see N below)
Input data
- I injector flowrate (cc/min)
- D engine displacement (cc)
- N number of injectors (piece, eg. 4 for a 4 cyl port injection)
req_fuel = D / N * 0.0012 / 14.7 / 0.755 / I * 60000
The constant 60000 is responsible for scaling output from min (coming from the injector cc/min) to msec unit we usually use for this. The other constants are self-explanatory.
Simplified equation is: req_fuel = 6.49 * D / N / I
Examples
| D | N | I | fuel pulsewidth (msec) | req_fuel=0x.. |
| 1600 | 4 | 220 | 11.8 | 76 |
We usually use 50% of calculated req_fuel and scale up VE values (j[] table) to double values (max values around 200, not 100) for somewhat higher precision.
Note: bin/req_fuel.pl in firmware has a bit more featureful calculator, and there are many on the web.
Tuning software support.
PSITuner implements a tool to calculate the req_fuel. In the Tools menu select "Fuel Calculations"
I just changed this to account for adding boost but Jorgen suggested that it's already taken care of. I'm not sure the right answer here as experimentally I found req_fuel=0x0d worked perfectly. As you can see the example screen cap yields a very similar value...
See also
- PortInjected/FuelInjectors
- GenBoard/VerThree/LowZInjectors
- OnlineCourse/InjectorOpening (advanced info for developers)