BPW and Injector math

[EagleMark]

Seems easy. But when I use Robert's numbers for the 3.1 from page 1 and work backward the constant works out to something like 906. 1461 / 3 does not equal 906. So maybe not so easy...

TBI V8 engine 1461.5

PFI V8 engine 365.375 which just happens to be 1461.5/4

PFI V6 engine 1461.5/3 = 487.166

3.1L engine (vol=.5231/rate=1.23) =.425284 * 487.166 = 207.12 which is pretty close to his 224 BPC! Figured at 43.5 PSI fuel pressure.

But if you use 48 PSI which I beleive is what MPFI pressure is without regulater it's even closer! 217 BPC to his 224!

Then consider the injector LB/HR I used are closely guarded secrets but accurateto calculations. Roberts 16.7 LB/HR may not be accurate, none of the TBI injectors are, but there's 10% possible difference as internet rumor...

Now if his injectors flowed actual 16.2 at 48 PSI and you do the calculation... guess what you come up with? 223.54 = his BPC of 224!

That book was worthless 2 years ago when I bought it... now it is starting to make sense. The answer to what 1461.5 is? AFR! BTW all those calcualtions are based on an AFR of 14.615

Which brings me to my next issue! Changing Stoich AFR in cal to match AFR of E fuel? Guess what? Need to recaculate 1461.5 before we do BPC/BPW...


SO if AFR of E fuel is 13.97 then the calculation would be:
TBI V8 = 1397.
PFI V8 = 349.25
PFI V6 = 465.66

[1project2many]

Are the TBI flow ratings wrong, or was a different pressure spec'ed for engineering when setting up the calibrations? Did GM / Delco flow them using gasoline or another fluid, such as Stoddard Fluid? This same road was travelled 15 years ago and IIRC injectors were checked. Final decision for me was to work out the flow rating from the calibration. I do as previously mentioned and scale the value whenever I can.

All I'm going to say about the math right now is this:
Picking different numbers to make the math work just isn't fair. Maybe Robert can chime in and give us the application that engine / cal is from and I can try with Delphi's published flow ratings.
No need to recalculate constant when AFR is a variable in the calibration.
It may be as simple as dividing constant by 3 or 4 but until I work out the whole equation I don't feel this has reached a conclusion. After all, the 7427 PFI conversion was supposed to be as simple as a jumper or two and a bit change but look how much effort's gone into straightening that one out.

[RobertISaar]

Picking different numbers to make the math work just isn't fair. Maybe Robert can chime in and give us the application that engine / cal is from and I can try with Delphi's published flow ratings.

example injector is a 91 pontiac grand prix w/3.1. was used on a LOT of 3.1 applications, probably some aluminum head 2.8 as well. GM defined the injector flowrate in a couple of locations in the BIN, two of which agree with the 16.7 lb/hr rating:

Injector Constant for Alpha-N Idle (KINJXBC5) = .2375 seconds per gram. (!!!) converting that into lb/hr = 33.42 lb/hr, but since the mode apparently is based off of single-fire calulcations, divide it by 2 to equal 16.71 lb/hr.

Injector Flowrate in Gallons per Hour (KDISFS) = 2.67 gallons per hour. converting that into lb/hr gives 16.70 lb/hr.



also, the 60V6 engines ran 43.5PSI at full pressure(until 99, i think, in 2000, they bumper up to ~52 or 55, i forget which)... pressure dropped from there with vacuum.

[EagleMark]

Well I didn't change any numbers to make it work up until Roberts injectors and fuel pressure to make it work. But here's how I came up with others

Part of the calculation given to us is in hacks, volume in liters of one cylinder liter/rate of one injector in grams per second. But I did increase precision by going 10 number past decimal point. Does not work at .1 need .1111111111
TBI V8 engine 1461.5 = 1 injector firing four cylinders

PFI V6 engine 487.166 = 3 injectors firing 3 cylinders, so one third the original 1461.5

PFI V8 engine 365.375 = 4 injectors firing 4 cylinders, so one fourth the original 1461.5

I suspect a SFI engine would be back to 1461.5 firing one cylinder per injector?

Back to TBI. Nothing was changed! These injector flows were all found in hacks and come out to 13PSI fuel pressure:
61 lb/hr (61.2#/HR) 7.71107029 gms/sec
76lb/hr (75.55#/HR) 9.519139876 gms/sec
80lb/hr (80.50#/HR) 10.1428293847 gms/sec
If you use those injector numbers the Grams/Second are accurate for one injector.

AND correct engine liters it comes out accurate to one cylinder liter!
5.7L 350 engine = 5.7329775012L / 8 for one cylinder.
7.4L 454 engine = 7.4390737152L / 8 for one cylinder.

Numbers come out perfect to BPC in bin...

All I have for 3.1L engine is 3.5 bore and 3.25 stroke = 3.1217081827L / 6 for one cylinder.

If the the 60V6 engines ran 43.5PSI at full pressure all the time? What would the difference in flow be with vacuum to without vacuum? Seems like the flow/pressure/differential is the only thing in question for the calculation? 207 is pretty close to 224 BPC?

[RobertISaar]

also, the 60V6 engines ran 43.5PSI at full pressure(until 99, i think, in 2000, they bumper up to ~52 or 55, i forget which)... pressure dropped from there with vacuum.

43.5 at no vacuum, they run a vacuum referenced FPR.

[EagleMark]

207 out of 224 is the best I can do? Wait? Is there any multipliers or for BPC? Like some do for EGR? What is EGR BPC?

[RobertISaar]

with the MPFI V6 stuff, there is no "EGR off BPC" and a table for when EGR is active like what is present in a few masks, there is only the table.

at 0% EGR, 224.
at 12.8% EGR, 187. stays at 187 from 12.8-25.4%, probably because EGR never really gets commanded above ~7% at most. almost perfectly linear change from 0 to 12.8%.

there are 3 tables that are multipliers to the BPC table result, one is vs baro, one is vs MAP/baro ratio, one is vs calculated intake runner temp. they interact with each other.... oddly.

[EagleMark]

That was my first impression... then came...

But looking at it airflow multiplier at 105 baro comes up to 0, then starts at 219 BPW Inverse... still pretty close to 217 I came up with.

If you do 95 baro and .25 you add 5.6 to 219 and get your 224...

Whats the BPW Offset vs BPW do?

BPW OFfset to battry voltage should be a zero at running voltage? How the heck are you supposed to figure that out? There's no Constqant to start with?