Saber008

Hello, recently I've been in touch with Injector Dynamics trying to figure out what to input as my base pressure for my 2002 NB Miata in their data spreadsheet calculator. I couldn't find the post before, but I do remember a member saying you can't just input 60psi for the non-manifold referenced fixed absolute pressure and stated you had to add idle vacuum to resulting in a higher base pressure to input into the data set. Opposite of what I heard from ID myself.

This is from Mitch at Injector Dynamics, who has been super helpful. I can't stress enough how great their support has been.
"I asked my boss (also does all of the tuning) and he said the best bet is to enter the data for where you'd be at idle, since correct injector data will matter the most at low pulsewidths. It'll be wrong everywhere other than idle, but that's what you'll have to deal with without a return style system.
​If you're at 60 psi you'll probably want to enter the data at somewhere around 50psi (not sure how much vacuum your engine makes at idle, but it will probably be close to that)."

For those that are using these injectors on a return-less fuel system it may be useful information.

irodd

iTrader: (4)

All said by Mitch from ID is correct except the math: 60psi-(10psi of vacuum)=70psi but not 50psi
see: Fuel Pressure Explained - Injector Dynamics
For non MAP referenced returnless fuel system differential pressure across the injectors=[fuel rail pressure]-[intake manifold pressure]
70psi at idle (60psi fuel rail -(-10psi intake vacuum)=70psi)
60psi at 100kpa (60psi-0psi=60psi)
45psi at 200kpa(60psi-15psi boost=45psi)
etc.

Saber008

Thanks for clearing this up. Makes perfect sense.

Hernj65

@irodd if I understand you correctly then has my deadtime been wrong this entire time on my nb returnless system? I have FIC 1000cc injectors and I have mspnp2 which is limited to deadtime at 13.2v. For deadtime I used the data they had for 4 bar 60psi. So if this is true my deadtimes and required fuel aren't correct? Or am I wrong?

irodd

iTrader: (4)

It would be nice to post here your settings.
But in general, MS2 has the limited settings for the injector characterization data, so you have 2 options:
deadtime@4bar (deadtime@idling will be compensated in VE map)
or
deadtime@5bar (deadtime @(everywhere except idling) will be compensated in VE map).
So, theoretically, both options are not 100% correct but from a practical point of view it does not matter.
Do not overthink it.

Hernj65

Yeah I've been way over thinking it honestly. My settings in ms2 are 1.195 deadtime and .180 for the correction. This is what I was told from a guy at FIC when I contacted them. It was really confusing what to put for the injectors because my data sheet didn't seem to coincide with what the guy at FIC told me. I have the data sheet if you wanted to look at it but no worries if not. I think it just comes down to the injectors for me. I should have either gone with ID1050x or smaller since I don't plan on big numbers. My choice on FIC was made from reading and asking around. I just feel like my power currently (around 225hp) makes the injectors struggle with how little duty cycle they see.

irodd

iTrader: (4)

Those numbers look correct for 4bar.

Hernj65

for sure thanks for the information!