IFR Delta Pressure and Scaling

[01maroonz2890]

Lurked on here many times but I finally have a question I'd like a concrete confirmation on. I'm working with a 2008 e38 that is hard coded to max out at 63.5 lb/hr. The car has h/c and e85 so it wont ever be boosted but I'm trying to scale in some of the new ID1050X using the stoich and ifr trick. The problem is that if I just double the stoich and half IFR I still am over the limit in a lot of the ifr table, I cannot also scale more than 2.18 because at that point I reach the 32 limit of the stoich table.

So heres a screen shot of what I did. I scaled the stoich by 2.15 to leave a little room down low and then applied the same ratio over the IFR table. It still does flat line way up top though. owever heres where my question comes in, does that even matter being NA? 58psi is 400kpa and assuming a worst case pressure differential it pushes to 500kpa. In that case all the cells that are flat lined shouldn't matter correct and I'm ok to run as is?

Thanks for the help

image.png

[DSteck]

You're never going to operate at the delta pressure that it maxes out, so stick to a scaling ratio of 2 and roll on.

[01maroonz2890]

that's what I originally wanted to do but if I do that I max out the Delta table between 464 and 480 kpa at 63.5. In theory couldn't the pressure delta go a little above that? Maybe I'm thinking about it wrong but I could have sworn I saw some people say 500 was possible with 58psi on an NA car. Is there any issue with using 2.15 as long as both tables are scalled with that factor? Obviously its a little more confusing but if that's what it takes... lol

[DSteck]

Your delta is always going to be under 460ish especially with a cam.

[07GTS]

its the injector flow rate at 58psi 400kpa at atmospheric pressure, if ur not boosted u will never go over atmospheric pressure so the 400kpa is your max

[07GTS]

dont forget to halve the IVT terms also, double stoich/halve IFR/halve IVT terms and your good to go

[01maroonz2890]

That's what I did in the top pic only I used 2.15 instead of 2 as the factor to get the range out further on the pressure delta.

I guess I'm just having a hard time understanding the relationship between the 400kpa (58 psi fuel pressure) and the actual map reading.

If the 400kpa is taken at atmospheric (which obviously wont go higher in an NA app), then what happens to the delta when the manifold is under vacuum? Like say you are idling at 35kpa where would that leave the pressure delta? Just trying to wrap my head around it ( I know its really simple)

Since it's a "delta" and atmospheric is 400kpa then a vacuum should be 500 I would think? That's what I've read anyway lol just confused a bit

[07GTS]

the gen4 uses delta pressure which is the difference between the fuel rail pressure and manifold pressure so its kept equal at all MAP readings, at idle u have a vacuum so that vacuum in kpa is taken off the 400kpa line pressure so the pressure at the injector tip is always the same, if u had a hose with water trickling out and u had to keep that at the same flow but u then added vacuum to it at the tip more water would come out then u wanted so u would have to slow it down to equal it out (same as what the table does smaller numbers for lower then 400kpa so it flows less fuel under vacuum) or the opposite if u had boost if u had 14psi line pressure and 14psi boost then u could open the injector and no fuel would come out because the pressure in the manifold equals the pressure in the fuel line,
or if u had a vac/boost referenced fuel reg and u watched that so at idle it lowers the fuel pressure and under boost it increases the pressure so the injector has the same delta at all times because the stock is a fixed fuel pressure this table does the same job as the referenced reg within the tune itself, vacuum is lower then 400kpa because its less pressure so closer to zero which is absolute vacuum

[01maroonz2890]

That makes perfect sense...here is where I'm confused though

IMG_5924.PNG

Motown I this thread says that values below 400kpa indicate boost and searching that around seems that other people say the same. Your claim makes more sense but it's odd that there's 2 completely different answers.

Let me ask this. If I left the ifr divide by 2.15 and the stoich multiplied by 2.15 is there any issue with doing that as opposed to doing it with the commons "half double" rule? I would think no because you're still keeping the relationship the same just wondering though

[07GTS]

if motown is talking 0 pressure then it must be the earlier OS they were different they used negative vac up to 0 which was atmospheric, the multiplier of 2 just keeps it simpler or u could do the 2.15 but there is no need

[01maroonz2890]

if motown is talking 0 pressure then it must be the earlier OS they were different they used negative vac up to 0 which was atmospheric, the multiplier of 2 just keeps it simpler or u could do the 2.15 but there is no need

Gotcha, I'm trusting you guys lol just going to do the 2 and see what happens for now. is there a pid to log that flow rate/pressure in the scanner? just would be curious to see

[07GTS]

yes think there are some IFR pids to log, don't forget your IVT also so it stays correct

[01maroonz2890]

Idle scan 1.hpl

ok so one more time lol I'm going to work on the car a bit today but her is a log a buddy sent me of his NA e38 car just at idle with the pressure delta logging. It looks like its always over 400 except at startup? is this just an odd case or?

[DSteck]

Want me to just set you up with a later ECM capable of twice the IFR?

[01maroonz2890]

Want me to just set you up with a later ECM capable of twice the IFR?

Sure pm me a price. Won't there be issues thought since this car is a silver blade and the later were gold?

[mowton]

That makes perfect sense...here is where I'm confused though

IMG_5924.PNG

Motown I this thread says that values below 400kpa indicate boost and searching that around seems that other people say the same. Your claim makes more sense but it's odd that there's 2 completely different answers.

Let me ask this. If I left the ifr divide by 2.15 and the stoich multiplied by 2.15 is there any issue with doing that as opposed to doing it with the commons "half double" rule? I would think no because you're still keeping the relationship the same just wondering though

It’s kind of like electron flow theory...there is a right hand and left hand flow theory...and both are recognized as correct….. In my explanation, 0 was used to define the atmosphere or in this case vacuum which in the PCM tables is like 80 kPa. In this context, 1 atmosphere is 14.7 psi (101 kPa) and represents naturally aspirated wide open throttle. Boost is greater than that. In our tuning world, vacuum can either be defined as 80 kPa (Gen III) or 480 kP (Gen IV). The Gen III context only takes te manifold pressure into consideration and we must adjust the IFR based on the fuel pressure being used in the setup. The Gen IV utilizes both the "push" from the fuel pump (i.e 400 kpa/58 psi) and the manifold pressure that the nozzle tip lives in. In this case vacuum, would be 480 kPa based on a 58psi/400 kPa fuel pressure and this is where I, along with all the others say you will never, ever need to go beyond so this is where you would only be concerned about exceeding the hard-coded limit.
Injectors are rated at 1 Atmosphere as well as a particular fuel pressure. You see that Ford injector data is rated at 39.15 psi while GM is normally 58 psi or 4 Bar. Some are even rated at 43.5 psi or 3 bar. These develop the initial flow rating that is used to calculate actual flow as the fuel and manifold pressures change. The higher the fuel pressure and/or lower the manifold, the higher the injector flows. The lower the fuel pressure and/or higher the manifold pressure, the less the injector flows.

The delta pressure approach was utilized to work with the new Supercharged setups like the ZR1 and ZL1 (E67) to allow fuel pressure to be varied to give the stock OEM injector a larger operating range. The fuel pressure is varied from low (idle/low load) to medium to High (boost) so the "Push" is changed and the PCM needs a means by which it can recalculate the actually IFR from the injector. If the fuel pressure is increased form 58 psi (400 kPa) to say 63 psi (434 kPa) by the FPCM, then the PCM uses the 434 and the MAP defines the nozzle environment so you can see if the MAP is reading 101 kPa (1 Atmosphere), then the delta pressure across the injector based on its rated flow is 434 kPa and the PCM can calculate the the accurate pulse width needed to provide the proper mass of fuel.

Hope this clears up my response

Ed M