Again, there are many ways to set up your testing, but this is a step I like to do that normalizes latency to a percent that can be compared quickly as a datum value. Flow latency is typically a few % higher than Physical latency, differences higher than 5% may be associated with injector flow non-linearity issues at other pulse widths, warranting further testing.
The rig as described up to this point, will at least get you a good idea of how much fuel is flowing and when it is flowing, but won’t tell you anything about where it is flowing. That is the subject of SAE J2715 (Port Injector Spray Measurement), so if you want to do more than spraying into a “patternator” (it’s like a glorified ice cube tray) for spray pattern measurement, you need this paper. If not, then at least inspect every injector spray head under a microscope. Late model multi-hole injectors incorporate angle cut holes for very precise vectoring to avoid wall wetting on the ports. If this type of injector has been modified by drilling out the spray holes, chances are it’s no longer vectored to the optimized spray pattern. This isn’t much of a problem at WOT, but can make tuning for sharp throttle response a whole bunch trickier. Spray vectoring is used to control cone angle, cone separation angle, off axis angle, and cone shape.
|Modern Spray plates are precision vectored to optimize atomization and avoid port wall wetting. Drilling out this spray plate would destroy this beautiful “Mirrored D” shaped vectoring! (Nissan VK56 injector by Denso.)|
So that’s the basics, other than finding a coefficient you will use to convert gram weight into a value that accurately relates to a particular flow rating system used to identify OEM type injectors you are involved with and to use the same on injectors you are testing. As an example, 1.333 * Grams of Mineral Spirits flowed at 68F is a good number that correlates to the middle of a large sampling of OEM injectors rated in cc/min. Start with 1.333 for a coefficient, keeping a box of “calibration injectors” locked away, retest them on a regular basis, and write down the date and flow data each time you flow them for consistency in your testing over time. A good practice is to flow a “calibration injector” at the beginning of daily testing and at the end of testing. If you are working with other groups that are also flow testing injectors, it’s a good idea to send them a few of your “calibration injectors” to flow on their rig, so you both are at least on the same page.
Safe Sex! Ok, bad metaphor, but if you have a good reputation as a tuner and you continue to just assume what’s up with the injectors when you tune, well then, not such a bad metaphor after all!
Order SAE J1832:http://standards.sae.org/j1832_200102/