Scaling injectors with new fuel pressure?

[minytrker]

I know how to scale them with stock psi, but what do you do when someone is running a higher psi system for boost?

[TAQuickness]

http://www.allmod.net/hpt/injectors.xls

[minytrker]

are you sure that right...it cant even get it to match my stock injector table

[joecar]

I know how to scale them with stock psi, but what do you do when someone is running a higher psi system for boost? You still use the spreadsheet to set the IFR, and then when you tune the 2 bar VE, the upper VE will take care of the fact that the IFR covers vacuum only (not boost).

If you want to be accurate, you can install a MAP-referenced pressure regulator (the regulator's pressure is adjusted by MAP vacuum/boost);

a MAP-referenced regulator keeps the pressure difference across an injector constant regardless of MAP vacuum/boost (it does this by adding MAP to the regulated absolute pressure, so MAP pressure is present on both ends of the injector and so subtracts itself out).

To calculate IFR for MAP-referenced regulator (flatline IFR table):
Flowrate = SQRT((P+BARO) / Rated_Pressure) x Rated_Flowrate
where pressure measured at rail with engine running is P+MAP, and from P+MAP subtract MAP and add BARO to get P+BARO.

Othwerwise, this is what the spreadsheet computes for an unreferenced regulator (sloped IFR table):
Flowrate = SQRT((P+BARO-MAP) / Rated_Pressure) x Rated_Flowrate
where pressure measured at rail with engine running is P, and BARO-MAP is manifold vacuum.

[joecar]

are you sure that right...it cant even get it to match my stock injector table
What are your numbers (rated flow, rated pressure, and rail pressure is 58psi)...?

[redhardsupra]

are you sure that right...it cant even get it to match my stock injector table
let me guess, was the car tuned by a 'professional' before? :)
and by that i mean did they tweak your IFR to get a quick'n'dirty dyno tune?

[minytrker]

nope i was going off my stock z06 injector table

[redhardsupra]

you sure you're doing it in right units? i've verified the few stock bin's against the number i get out of the spreadsheet and they all check out just fine.

[TAQuickness]

miny - how far off are the numbers? IIRC, they won't be exact due to the way the PCM stores them.

[joecar]

What are your numbers (rated flow, rated pressure, and rail pressure is 58psi)...?
Post your numbers and an image of your IFR table.

[minytrker]

29.142278
29.328292
29.514307
29.700321
29.886336
30.010345
30.196360
30.382375
30.568389
30.754404
30.940418
31.064428
31.250442
31.436457
31.560467
31.746481
31.932496

[joecar]

What are the rated flowrate/pressure values for your injectors...?

[minytrker]

28.8
58 psi at fuel rail

[joecar]

Injectors rated 28.8 lb/hr at 58 psi; running 58 psi on your fuel rail, I calculate the following:

28.8000
28.9795
29.1579
29.3352
29.5114
29.6866
29.8607
30.0339
30.2061
30.3772
30.5475
30.7167
30.8851
31.0525
31.2191
31.3847
31.5495

Your numbers a little higher, how'd you calculate those...?

[minytrker]

Those are the stock values.

[DrX]

You still use the spreadsheet to set the IFR, and then when you tune the 2 bar VE, the upper VE will take care of the fact that the IFR covers vacuum only (not boost).

If you want to be accurate, you can install a MAP-referenced pressure regulator (the regulator's pressure is adjusted by MAP vacuum/boost);

a MAP-referenced regulator keeps the pressure difference across an injector constant regardless of MAP vacuum/boost (it does this by adding MAP to the regulated absolute pressure, so MAP pressure is present on both ends of the injector and so subtracts itself out).

To calculate IFR for MAP-referenced regulator (flatline IFR table):
Flowrate = SQRT((P+BARO) / Rated_Pressure) x Rated_Flowrate
where pressure measured at rail with engine running is P+MAP, and from P+MAP subtract MAP and add BARO to get P+BARO.


This is what I have done but the PCM uses a sloped extrapolation once I go off the table(boost) according to the logged IFR PID. So much for accuracy. Must be written into the OS.

[joecar]

This is what I have done but the PCM uses a sloped extrapolation once I go off the table(boost) according to the logged IFR PID. So much for accuracy. Must be written into the OS.
How does the PCM extrapolate the IFR...? I thought if it was flat horizontal then the extrapolation would be the same.

I'm not sure which pid this is, I couldn't see it; can you post a pic of your logged chart.

[DrX]

How does the PCM extrapolate the IFR...? I thought if it was flat horizontal then the extrapolation would be the same.

I'm not sure which pid this is, I couldn't see it; can you post a pic of your logged chart.


This is what I would like to know.

GM.INJFLOW- Calculated injector flow rate

Not much to see on the chart as the IFR only drops 4.6% by the time I reach 165kPa MAP. The plot is pretty much a flat line. It starts at 8.89g/s(as per my IFR table) and falls to 8.48 g/s

[joecar]

Post a pic of your B4001 IFR table.

[DrX]

Post a pic of your B4001 IFR table.

B4001

[joecar]

Interesting, I would have thought that the extrapolation of a flat horizontal line would have been the same flat horizontal line.

I PM'd Paul asking how GM.INJFLOW is looked up:

Yes, the GM.INJFLOW PID is the product of B4001*B4002.
I assume your B4002 "Injector Voltage Corrections" is also flat...

So, you and I are both wondering what is going on here... :nixweiss::bawl:

[joecar]

I assume your B4002 "Injector Voltage Corrections" is also flat...This won't matter any since the alternator would be putting out a constant voltage at that time.