[montauk]

Thanks for posting this. I appreciate it.
Dave

Originally Posted by Rivet

On a speed density (a true volumetric efficiency fuel model) system you have to tell the ecu what the fuel pressure is either by inserting that pressure manually or having a fuel pressure transducer to feed the pressure in real time to the ecu, along with as complete as possible injector characterization, fuel choice chemistry, etc so that it ultimately knows the exact fuel mass being injected into the motor per injector pw.

The VE table in conjunction with environmental data and engine size is to tell the ecu how much air mass is in the combustion chamber.

And the Lambda table ultimately dictates what the end PW will be to meet the target air/fuel mixture.

I say all this in simplistic form as there are plenty of resources that explain in greater detail by people that are blessed with gifts in communication.

If you adjust the fuel pressure without telling the ecu that the operating fuel pressure has changed then it will have a direct effect on lambda (air/fuel mixture) that would require a VE table change to meet target since the ecu has no idea what the actual fuel mass is anymore. If you had a transducer on the fuel rail feeding the pressure in real time into the fuel calculation OR update the fuel pressure value to what guage pressure is then the adjustment in pressure will not have an effect on the air fuel mixture or the value in the VE table as the calibration will change the PW to meet the target lambda in the background.

With that being said, increase in fuel pressure from a semi typical 3 bar relative pressure will have greater atomization generally but that does depend on the injector design as well and when you get to the point of diminishing returns as an increase in pressure will also heat the fuel more, increase amperage at the pump and decrease flow at the pump which is fine if you have enough head room flow wise with your pump choice and you have wiring appropriate for the amperage the pump runs.

I highly recommend a fuel pulse damper on a dead headed rail and still recommend them for a flow through rail. You can tune around the injector pulse width "hammering" in most cases but the VE table will end up ugly as all hell and will not represent the true air mass in the motor at smaller pulse widths.

And another small point with regards to the injectors themselves. A good injector company will provide data that will encompass dead times and flow at various fuel pressures and voltages if that injector was designed for aftermarket use (i.e Injector Dynamics). If the injector was originally spec'd for an OEM manufacture then that injector data is proprietary and will not be shared so you have to either go by data provided by the internet which is highly suspect usually, provided by a vendor, or send them out to be characterized. Also this data changes depending on the hardware of your chosen ECU as not all injector drivers operate the same, this is a big selling point to Injector Dynamics as they provide ECU specific characterization data.