BPW and Injector math

[EagleMark]

Found some interesting things in another thread.
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?1601-BPC-question.-Can-you-check-my-math-7060-85&p=19832&viewfull=1#post19832

Maybe we can find out why? Could use someone with actual math skills as well as spreadsheet skills to apply what we find. I have plenty of starter spreadsheets but some are off, some are incomplete.

Here is what I found in hacks.



TBI 5.7L 61 lb/hr = 61.2 lb/hr $0D states injector size is 61 lb/hr
Val = 1461.5 * (VOL/RATE)
VOL = Vol of 1 Cylinder in liters, (0.7125L)
RATE = Injector flow in gms/sec 5.7l = 7.71 gms/sec (61.2#/HR)
(VOL/RATE) = 0.0924 l/gm/sec
= BPW 135 set in $42 bin file and correct


TBI 7.4L 76 lb/hr = 75.55 lb/hr
Val = 1461.5 * (VOL/RATE)
VOL = Vol of 1 Cylinder in liters, (0.930L)
RATE = Injector flow in gms/sec 7.4L = 9.52 gms/sec (75.55#/HR)
(VOL/RATE) = 0.09768 l/gm/sec
= BPW 142 set in $85 bin file and correct.


TBI 7.4L 80 lb/hr = 80.50 lb/hr
Val = 1461.5 * (VOL/RATE)
VOL = Vol of 1 Cylinder in liters, (0.930L)
RATE = Injector flow in gms/sec 7.4L = 10.144 gms/sec (80.50#/HR)
(VOL/RATE) = 0.091679 l/gm/sec
= BPW 134 set in $42 bin file and correct.

[RobertISaar]

any mask that uses a BPC/BPW is really a fudge to being with... trying to use that conversion for MPFI engines doesn't work at all, last time i remember trying to do it.

example: 3.1MPFI 60V6 = 16.7 lb/hr injectors(6 of them, obviously), factory BPC at 0% EGR is 224.

.517 L/cyl volume
2.1 grams/sec per injector

.517/2.1 = 359.8

i really can't come up with a reason for a BPC of 224 using that calc... making the injectors "appear" as a TBI setup could be done by multiplying flowrate by 3, so that it will seem like 2 50.1 lb/hr injectors, the calculated BPC comes out to 119.9....

if you then try to account for the injector firing scheme(alternating TBI(two injections from all injectors per revolution???) vs double-fire MPFI(one injection from all injectors per revolution)), i guess you could multiply the 119.9 by 2 to come up with 239.8, which is at least somewhat close to the factory BPC of 224, it's off by 7%, which is within O2 correction range.



in any case, i just take known values and multiply or divide depending on difference in displacement or flow... tends to work out pretty well.

[RobertISaar]

and that conversion is curious.... move the decimal place over twice and it's almost the exact stoich ratio for E0 gasoline...

[EagleMark]

Problem with the old calculator was it read wrong if fuel pressure was same in both? I spent the day learning Open Office version of Excell... have it working properly except a way to get new injector flow from old pressure new pressure? Can't figure out how it was done?

=ROUND(SQRT(new pressure/old pressure)*injector lb/hr;2) What does ;2 do? Or what would be another way to do this?

[dave w]

The attached file (Excel) is what I use to figure BPW. I use injector flow and engine displacement as the variables.

dave w

[chevmasta]

That is the calculator I used (from dave w) to calculate my 120 in the other thread....

[dave w]

The attached file (Excel) is what I use to figure BPW. I use injector flow and engine displacement as the variables.

dave w

An example pic:

I'm often challenged with BPW. It seems it's apples, oranges, and bananas...what injectors are rated to flow (apples), what injectors actually flow (oranges), and what is programmed into the .bin (drives me bananas:mad1:).

dave w

[EagleMark]

I got the numbers to add up to what GM starts with, problem is 2 fold.

Liter per cylinder
5.7L is 5.73L
7.4L is 7.44L
So now when you convert engine liter to cylinder liter it adds up.

Injectors
61 lbhr is 61.2 lb/hr
74 lb/hr is 75.55 lb/hr
80 lb/hr is 80.50 lbhr
SO now when you convert to grams/second they add up.

My problem now is what pressure did these start with? We can assume 13, 12 may be better. But I don't think adding pressure on top of that a calculating by percent of increase is accurate?

This was in one of my spreadsheets.
=ROUND(SQRT(new pressure/old pressure)*injector lb/hr;2) What does ;2 do? Or what would be another way to do this?

[EagleMark]

And Greg has corrected us from following internet protocol. This has always been mis titled even in hacks back to 90s as BPW when it is the BPC.

[RobertISaar]

http://witchhunter.com/injectorcalc1.php

i just use the bottom calculator to determine new flowrate... but since you're not 100% on the original pressure, that throws a rather large wrench into the machine.

[EagleMark]

That, like so many MPFI calculators doesn't work. Change the old pressure to anything and old flow rate never changes?

[RobertISaar]

well, no, old isn't supposed to change... you're supposed to put in known flow and pressure ("old") and a new pressure that you want to run them at, and it will spit out a new flowrate.

[EagleMark]

Ah.. I see, they should move the calculate button down, you need to fill in three spots, not 2... OK. I'm not real brite when it comes to something set up to confuse in first place.....

[EagleMark]

Now that I can use it correctly it does calcaulate to same numbers I'm getting in spreadsheet.

Still don't know what the ;2 does in equation?

=ROUND(SQRT(new pressure/old pressure)*injector lb/hr;2) What does ;2 do? Trying to learn Excel...

[RobertISaar]

i've never used a semi-colon in an equation in excel or it's equivalents... i've got no idea.

[dave w]

Here is something I quickly put together.

dave w

[chevmasta]

Here is something I quickly put together.

dave w

Since I'm not very good with excel.....

Can you put the BPW calculator in your previous post, this fuel pressure flow change calculation, and the IDC flow calculation all into one excel spreadsheet?

[4 * IPW (ms) * RPM]/1200

[EagleMark]

I've got about a bazillion hours into learning spreadsheets. Almost 13 hours into edits in this one recorded in the file.

Special Thanks to Dave W at Old School EFI for sharing his BLM spreadsheets, they are all included.

For evaluation only! I've tested till I'm blind and it all seems to work properly. Warning, spreadsheet on steroids! If it passes inspection I think it's worthy of GearHead-EFI.com name...

EDIT: New upload with protection issue on Injector Duty Cycle fixed.

[dave w]

I've got about a bazillion hours into learning spreadsheets. Almost 13 hours into edits in this one recorded in the file.

Special Thanks to Dave W at Old School EFI for sharing his BLM spreadsheets, they are all included.

For evaluation only! I've tested till I'm blind and it all seems to work properly. Warning, spreadsheet on steroids! If it passes inspection I think it's worthy of GearHead-EFI.com name...

I'll try to review the above attached spreadsheet...I have excel not Open Office. See attached screen shot.

dave w

[EagleMark]

Hmmm... Open Office opens all Excel stuff. It can also save as .xls so here it is.

[dave w]

Hmmm... Open Office opens all Excel stuff. It can also save as .xls so here it is.

Much better! I can see the formulas in the individual cells with the .xls file format.

dave w

[chevmasta]

I have excel too.

I tried plugging some numbers in but nothing changed. are these two not compatible in that way? (preface: imanidiot)

....and you just posted it.... LOL!

[chevmasta]

Thankyou for that sheet Mark.

I've only tuned my truck.......but I do have a couple people interested in me helping their trucks out and that spreadsheet will be most helpful!

It's really cool to have a community like this one. :)

[dave w]

Hmmm... Open Office opens all Excel stuff. It can also save as .xls so here it is.

I've been challenged with the question on IPW. I noticed the attached spreadsheet is write protected for Injector Duty Cycle (IDC) MPFI vs TBI. To correctly calculate IPW TBI vs. MPFI (IDC) is required. So I'm wondering why IDC is write protected.

dave w

[EagleMark]

I protected everything so people would not change the cells that were not in White! There is no password, in Open Office just click Tools, Protect Document and Sheet to turn off protection. I assume Excell is similar?

[dave w]

I protected everything so people would not change the cells that were not in White! There is no password, in Open Office just click Tools, Protect Document and Sheet to turn off protection. I assume Excell is similar?

The Excel message I posted states how to disable write protection. I was hoping to help others who might encounter the same write protection message.

I'm wondering where the formula for injector bias was sourced from? Some TBI definitions don't show an injector bias ($85, $OD, $OE, $E6, $31 $61, $62)? I think $42 usually has 454 injector bias @ .276 and 350 injector bias @ .375? I'm wondering if changing injector bias will affect injector flow?

dave w

[EagleMark]

Added to the total BPW. used to compensate for injectors that open slowly. As the fuel pressure is increased the injector takes longer to open. If you add fuel pressure this should be increased.

Injector bias is in $42, $85, $61 and all the older ECM that have a BPW/BPC. Notice these do not have Cubic Inch or any displacement or Injector size? It is calculated by engine size in liters / 8 so volume of one cylinder, divided by rate of injector at grams/second = vol/rate * 1461.5 = BPC

TBI 5.7L 61 lb/hr = 61.2 lb/hr $0D states injector size is 61 lb/hr
Val = 1461.5 * (VOL/RATE)
VOL = Vol of 1 Cylinder in liters, (0.7125l)
RATE = Injector flow in gms/sec
5.7l = 7.71 gms/sec (61.2#/HR)
(VOL/RATE) = 0.0924 l/gm/sec
= BPW 135

It is not in newer PCM like $0D which does not have BPW/BPC. The starting BPC is calculated by injector size and Engine displacement that those masks have.

But there's much more to BPW/BPC that I have not figured out the math for yet!!! If you stick to the guidelines this is not an issue. But you know yourself and I and others have had this discussion on cheating and adding BPW/BPC for more fuel. My tests showed that to work to some extent but fall apart at higher RPM/Load if raised and I found out why. Injectors go static at about 150 BPW/BPC at 3600 RPM!!! Base Pulse Width is time injector is open compared to how much time is available at RPM, so back to why Duty Cycle is so important, Injector Pulse Width in percent of time open in M/Sec changes with RPM = time gets shorter. But if we could do the math we would find a direct correlation from Injector Duty Cycle to BPW/BPC.. constant.

[1project2many]

But if we could do the math we would find a direct correlation from Injector Duty Cycle to BPW/BPC.. constant

Say this differently... what are you looking for? The BPC alone won't give you IDC because injector pulsewidth is a function of the air calculation. Are you trying to estimate how much the BPC can be adjusted without going static?

[EagleMark]

Are you trying to estimate how much the BPC can be adjusted without going static?Yes! There has to be a point where it is static... right? RPM...

[RobertISaar]

this would be my first guess for estimating where going static would occure:

find RPM with highest injector duty cycle, let's say it's 75%.

now, you know you can run up to 25% more fuel before you run into 100%DC, though you may go static before then, but for theoretical purposes, 100% is the target. take your BPC and multiply it by 1.25 (to make it 125% of it's original value), and then you SHOULD hit 100% DC in the otherwise identical condition, assuming the O2 sensor doesn't cause a significant reduction to base fueling.

[chevmasta]

Yes! There has to be a point where it is static... right? RPM...

It's going to be different for every engine (atleast modified). The biggest variable will probably be Volumetric Efficiency (and engine displacement). Then also RPM.

VE
Cubic Inches
BSFC
RPM
Injector size (flow)
Bias or latency
NA or Boosted

soooo many variables!

[gregs78cam]

this would be my first guess for estimating where going static would occure:

find RPM with highest injector duty cycle, let's say it's 75%.

now, you know you can run up to 25% more fuel before you run into 100%DC, though you may go static before then, but for theoretical purposes, 100% is the target. take your BPC and multiply it by 1.25 (to make it 125% of it's original value),


Actually in this 75% DC scenario you would want to multiply your BPC by 1.33333. Basically the inverse of number. As an example lets say you were at BPC of 75, and were hitting 75% DC, you would divide 100 by the percent you are at and multiply your BPC by that.

[dave w]

I've been thinking Marks spreadsheet is a guideline, to help figure out an appropriate injector for a given engine application. IMHO, the practical limit for two 90 lb TBI injector is about 400 HP +/- 5%. I think the calculations in Marks spreadsheet help both the engine builder and EFI Tuner understand what would be required from the EFI system on a performance engine. The old saying, "Do the Math", IMHO Marks spreadsheet does the math!:thumbsup:

dave w

[RobertISaar]

Actually in this 75% DC scenario you would want to multiply your BPC by 1.33333. Basically the inverse of number. As an example lets say you were at BPC of 75, and were hitting 75% DC, you would divide 100 by the percent you are at and multiply your BPC by that.

possibly, i don't remember off-hand, i'd have to fire up my bench and switch between two BPCs to see what the effect on BPW(and therefore IDC) is.

[gregs78cam]

possibly, i don't remember off-hand, i'd have to fire up my bench and switch between two BPCs to see what the effect on BPW(and therefore IDC) is.

Well yea, I was just saying that the math is done this way, to get from 75% to 100%. I have no idea what the real correlation is or how the ECM will change the Injector PW.

[EagleMark]

I've been thinking Marks spreadsheet is a guideline, to help figure out an appropriate injector for a given engine application. IMHO, the practical limit for two 90 lb TBI injector is about 400 HP +/- 5%. I think the calculations in Marks spreadsheet help both the engine builder and EFI Tuner understand what would be required from the EFI system on a performance engine. The old saying, "Do the Math", IMHO Marks spreadsheet does the math!:thumbsup:

dave wWoo Hoo!

Usually I make a fool of myself first shot! :rolleye:

[EagleMark]

Greg and Robert. Your theories are all good, but I was looking for something different. Not a test on when they go static.

A mathmatical equation for the BPW/BPC. Since all the Sync/Async settings are in Usec and Msec there has to be something?

BPW/BPC = 1461.5 * (cyl size / gm/s of fuel) so what is 1461.5 ?
In a 5.73L engine comes out to 135 BPW/BPC.

So... BPW/BPC = 1461.5 * (cyl size / gm/s of fuel) = 135. Where is 100%? Although they may go static at 85%... because the off time is more important then on time at the high end.

[gregs78cam]

So you want to see the equation that the ECM uses to come up with Injector PW?

The only way to know what 100% Injector DC is, would be to use the same equation that the ECM uses to calculate Base Pulsewidth, plus all of the adders; i.e., Temp, Load, RPM, TPS, too many variables that are always changing.

[1project2many]

Yes! There has to be a point where it is static... right? RPM...
Yes. It's when the airflow is equivalent to the point at which the desired AFR requires the injectors to be on full time...
Translation? Run a dyno simulation. Where the predicted HP is equal to injector flow, you're done.

Think backward... injector is static at 100% DC. What's the fuel flow at that DC? What HP can it support? If the engine flows more air than that then it will starve for fuel.

Put a pair of 20#/hr injectors on a big block and you'll be out of fuel somewhere just off idle, right? But... what if your cam has only .100" lift??? The injectors will provide plenty of fuel. You can't know what the engine needs for air while you're trying to tune the engine for fuel.

If the VE table is already tuned you can work the calculation backward to see if the injector will go static. But, how could you tune the VE table without the injector?? All I can think of, at least for us mortals, is simulation software.

I suppose if you're in the process of tuning and you're seeing the VE tables climb toward 100% then you could make an estimate to see if changing the BPC will be enough. But if you calculated the BPC correctly then the fact that you're nearing 100% VE already tells you the injector's not really large enough.

It would be good to have the fuel equation broken out and we might be able to make some neat tools if it were. I think your observation that BPC shouldn't be moved more than a small percentage is perfect. If you're tuning and VE is climbing above 100%, you really need to change the fuel pressure or the injectors then recalculate BPC for the new injector flow.


BPW/BPC = 1461.5 * (cyl size / gm/s of fuel) so what is 1461.5 ?
In a 5.73L engine comes out to 135 BPW/BPC.

I haven't had time to look at this but it's not the same for PFI engines (Reference ECMGuy's ASDZ hac), and it appears that it's different again for the V6 pfi. I'm looking at chapter 4 of Greg Banish's book on Google Books. The answer is probably there if I can find time to read through it.

[EagleMark]

I haven't had time to look at this but it's not the same for PFI engines (Reference ECMGuy's ASDZ hac), and it appears that it's different again for the V6 pfi. Well differant but same as I compared TBI and PFI.

TBI
; Val = 1461.5 * (VOL/RATE)

PFI
; Val = 365.375 * (VOL/RATE) 365.375 x 4 = 1461.5 so 4X as many injectors!

Reading Greg Banish book is making my head hurt! :laugh: But your right, I think it's there.

But one of the first things in calculation is AFR. 1461.5 / 100 = 14.615 AFR... so right there BPW/BPC calculation would need some adjustment to handle 12.5 AFR.

Still working on it but I really think that BPW/BPC could be used as a calculation of Injector Duty cyle at which static with RPM could be used as a guidline. It should come out to 100%, but we know that 85% of that is usable as we need off time or static is an issue...

[1project2many]

TBI
; Val = 1461.5 * (VOL/RATE)

PFI
; Val = 365.375 * (VOL/RATE) 365.375 x 4 = 1461.5 so 4X as many injectors!


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...

That book is definitely crammed full of engineer speak. Maybe he thinks he's making it easy for us... :)

You're right... we could calculate the maximum rpm available to the injector based on the number of times the injector is turned on. But that doesn't tell us where the injector will actually go static based on VE table.

[EagleMark]

That book is definitely crammed full of engineer speak. Maybe he thinks he's making it easy for us... :) Sure makes himself look as smart as he is! Hard for a normal GearHead Tuner to convert...

[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...
:mad1:

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

:popcorn:

[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.

http://i.imgur.com/WkOPHQH.png

[EagleMark]

:laugh:

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

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?

[RobertISaar]

the inverse table is simply a multiplier for accounting for estimated intake runner temp airmass correction, i just never entered the equation(the one GM supplied was.... useless)

the way those all interact with A1:

BPC vs %EGR of airflow value is looked up, saved twice.
airflow multiplier vs MAP/baro ratio is looked up and multiplied with one of the BPC vs EGR% values, value is then saved.
airflow multiplier vs baro is looked up and multiplied with the same modified BPC vs EGR% value.
then the unmodified BPC vs EGR% value is pulled and added to the modified value and saved.

that value is used for the basis of the speed-density calculation(i refer to it as "airflow", but it's not really)

so, that value and the target AFR get mixed in interesting ways and form the "fuel required" value.
that value then gets VE correction.
that value then gets MAP correction.
that value then gets intake runner temp correction.

now the value is the base pulse width before O2/closed loop and injector offset correction.



so, those 4 tables i posted about are ACTUALLY used as an adder for the BPC value, they can never be subtractive. honestly, i'm amazed it works as well as it does, but i still want to scrap it all for a real speed-density derived airflow / fuel required value.

[1project2many]

Those are factory tables? Is MAP / BARO ratio table actually MAP / BARO in code? Is that the leftmost table, which has entries from 0 to .5? And is that value frequently calculated based on current MAP readings or is it a correction that's only updated if BARO is updated?

Also, is there a coolant temp correction or an inverse AFR multiplier?

Edit: Mark.. is VE part of the $42 ALDL data? If not that's an easy way to see if tables are maxed while tuning. Total VE is saved at $00A9

[EagleMark]

Edit: Mark.. is VE part of the $42 ALDL data? If not that's an easy way to see if tables are maxed while tuning. Total VE is saved at $00A9That could be another hack!

But the purpose here was not to figure out how once tuned, it was to avoid it by calibrating a tune in the first place. I still think theres a clue in BPW (now known as correct BPC) as far as RPM. Seems a smaller number BPC will rev higher, increase pressure, recaculate BPC and number gets smaller was my first clue, then seeing $85 7.4L BPC at 142? Higher then other BB with bigger injectors at BPC 134... well it's hitting %85 Injector Duty Cycle at 3500 PRM and BLM go lean.

I think BPC of 135 is 13.5 Msec

[EagleMark]

Here's some convincing numbers. In another thread a 7.4L engine with 74 (75.55)lb/hr injectors and BPC set to 142 from factory.

He is having BLM issues at higher RPM and reported 7.05 Msec at 3600 RPM. Using the formula in calculator
TBI IDC (%) = [4 * IPW (ms) * RPM]/1200
7.1 M/sec, 3600 RPM set to TBI is 85.2% Injector duty cycle.

If you use the MPFI formula
MPFI IDC (%) = [2 * IPW (ms) * RPM]/1200
on his BPC of 142 which I still believe is M/sec so 14.2 at 3600 RPM guess what? Same 85.2% Injector Duty Cycle!

Is it because of TBI injector firing strategy compared to MPFI strategy that this works? What cuts BPC in half for injector duty cycle? 2 injectors? Firing? DRP? Could also be the reason these systems go Async after it runs out of Sync fuel for higher load needs?

If you use a lower BPC of 125 = M/sec 12.5 at 3600 RPM it goes down to 75%...

To get to 5000 RPM and stay under 85% Injector Duty Cycle you need a BPC of 102! Seems to be working...

So it's looking like calculating BPC for higher fuel pressure is not only correct, but the lower BPC is also needed for higher RPM?

[1project2many]

If he's at 85% IDC then the injector is too small. BPC, VE, BARO, CTS correction... all work together to come up with injector "on time." If the BPC is wrong, then during tuning the VE tables will "automagically" get adjusted wrong in the other direction and make up much of the difference. At the end of the day, tuning for AFR and best timing, no matter how you play with the variables you'll hit the same wall. 85% IDC. It's just robbing Peter to pay Paul.

BPC may work out to a time value. You can use Excel to see required BPC for a specific engine size, VE, and AFR. This one also helps visualize IDC.

[RobertISaar]

Those are factory tables? Is MAP / BARO ratio table actually MAP / BARO in code? Is that the leftmost table, which has entries from 0 to .5? And is that value frequently calculated based on current MAP readings or is it a correction that's only updated if BARO is updated?

Also, is there a coolant temp correction or an inverse AFR multiplier?

Edit: Mark.. is VE part of the $42 ALDL data? If not that's an easy way to see if tables are maxed while tuning. Total VE is saved at $00A9

all factory values.

MAP/baro ratio is exactly as it sounds, MAP and Baro get loaded, then divided, then the result of that is the MAP/baro ratio. yes, it's the leftmost table.

coolant temp correction / inverse AFR multiplier?c

oolant temp is accounted for in the intake runner temp calculation, where it's used with IAT, airflow and a couple of other values to estimate airmass temp by the time it gets into the cylinders.

inverse AFR... that might be the rightmost table loaded, using the equation given by GM, it gaves values in *Kelvin, which was pretty useless to me once i looked at the code and determined the table value was simply used as a multiplier.

[EagleMark]

If he's at 85% IDC then the injector is too small. .What's strange about 7.4L $85/$D8 bins is BPW was 134, then later 142! I beleive this was the year 7.4L changed from 80 to 76 lb/hr injectors. This is also the mask that was $85 BCC Axxx that was all superceeded to $D8 Bxxx.

[chevmasta]

That could be another hack!

But the purpose here was not to figure out how once tuned, it was to avoid it by calibrating a tune in the first place. I still think theres a clue in BPW (now known as correct BPC) as far as RPM. Seems a smaller number BPC will rev higher, increase pressure, recaculate BPC and number gets smaller was my first clue, then seeing $85 7.4L BPC at 142? Higher then other BB with bigger injectors at BPC 134... well it's hitting %85 Injector Duty Cycle at 3500 PRM and BLM go lean.

I think BPC of 135 is 13.5 Msec


Here's some convincing numbers. In another thread a 7.4L engine with 74 (75.55)lb/hr injectors and BPC set to 142 from factory.

He is having BLM issues at higher RPM and reported 7.05 Msec at 3600 RPM. Using the formula in calculator
TBI IDC (%) = [4 * IPW (ms) * RPM]/1200
7.1 M/sec, 3600 RPM set to TBI is 85.2% Injector duty cycle.

If you use the MPFI formula
MPFI IDC (%) = [2 * IPW (ms) * RPM]/1200
on his BPC of 142 which I still believe is M/sec so 14.2 at 3600 RPM guess what? Same 85.2% Injector Duty Cycle!

Is it because of TBI injector firing strategy compared to MPFI strategy that this works? What cuts BPC in half for injector duty cycle? 2 injectors? Firing? DRP? Could also be the reason these systems go Async after it runs out of Sync fuel for higher load needs?

If you use a lower BPC of 125 = M/sec 12.5 at 3600 RPM it goes down to 75%...

To get to 5000 RPM and stay under 85% Injector Duty Cycle you need a BPC of 102! Seems to be working...

So it's looking like calculating BPC for higher fuel pressure is not only correct, but the lower BPC is also needed for higher RPM?


If he's at 85% IDC then the injector is too small. BPC, VE, BARO, CTS correction... all work together to come up with injector "on time." If the BPC is wrong, then during tuning the VE tables will "automagically" get adjusted wrong in the other direction and make up much of the difference. At the end of the day, tuning for AFR and best timing, no matter how you play with the variables you'll hit the same wall. 85% IDC. It's just robbing Peter to pay Paul.

BPC may work out to a time value. You can use Excel to see required BPC for a specific engine size, VE, and AFR. This one also helps visualize IDC.


What's strange about 7.4L $85/$D8 bins is BPW was 134, then later 142! I beleive this was the year 7.4L changed from 80 to 76 lb/hr injectors. This is also the mask that was $85 BCC Axxx that was all superceeded to $D8 Bxxx.

Mark is talking about this thread:
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?1601-BPC-question.-Can-you-check-my-math-7060-85

This is where I'm at 85% IDC. Which seems weird considering the truck engine is mostly stock minus headers and an exhaust. Fuel pressure has ben adjusted from 12psi to 16psi.
I'm currently going to try to raise my BPC to 150 and retune my VE table and see where I end up.....up top. Mind you im not "that" lean. Up top a BLM of 131 (BUT im only at 58% throttle.......I just realized). In PE mode I sure would think it would run out of fuel...........but I don't have any knock counts at WOT thank God.

Mark,
Just for clarification. I'm using the $85 mask with a BANC.bin
Should I be using the $D8 mask becuase of the superceed? Will it make a difference?

[EagleMark]

Mark,
Just for clarification. I'm using the $85 mask with a BANC.bin
Should I be using the $D8 mask becuase of the superceed? Will it make a difference?Stick with $85, there's a few issues with $D8 tables I never fixed when I found all Axxx bins were superceeded to Bxxx bins, although all I have seen they are identical except $D8 has governer paremeters. It would take some work but they need to be combined.

[gregs78cam]

Just to double check the Advanced $0E that I am using, what should the conversion/equation be?

[EagleMark]

(X*4*Y)/1200

X= BPW and Y=Engine RPM.

TBI IDC (%) = [4 * IPW (ms) * RPM]/1200

Wrong calculation was started here in 2007:
http://www.fullsizechevy.com/forum/general-discussion/performance/tbi-tuning-87-95-obd-i-ecm-pcm/297086-calculating-injector-duty-cycle-injector-pulse-width.html

Comes out correct to 1project2many TBI helper and all other math...

[gregs78cam]

Ok, so to simplify = X * Y / 300

My $0E shows X*Y/600, HHMMMMMM, I might need more pressure after all.

[EagleMark]

:rolleye:

You know your better at math then me... :thumbsup:

But you got a lot of injectors too! They fire same as TBI right? Here's MPFI
MPFI IDC (%) = [2 * IPW (ms) * RPM]/1200

Try out my new spreadsheet calculator, put your math skills to good use and read this thread too, here's direct link to spreadsheet:
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?1609-BPW-and-Injector-math&p=20070&viewfull=1#post20070

[gregs78cam]

I'll take a look at it. Yes they fire just like regular TBI, just alternate opposite of each other.


EDIT: Looks pretty good Mark, you're right that first page is a lot to take in. Only recommendation I have is to label the '7247 stuff as "$0D/$0E". Oh and yes I need more pressure.:thumbsup:

[EagleMark]

I moved these fuel pressure posts here Greg...

There's some polishing to do, thanks for the mask names on sheets. It's a lot of info, but all you have to fill in is White Boxs first set. Last st are optional calculations.

Were you happening to run up to 49% IDC on the old one?

[gregs78cam]

I would have to fire up the laptop, and check a log, but I am pretty sure I was hitting around 38% (would really be around 80%) and IPW would not go higher than 4.2ms, which is fine at 4K rpm but not at 6K.

[JeepsAndGuns]

I am really super lost in this thread and its all 99% over my head. But did I read something right, saying that the injector duty cycle % display in the 0D ADX is wrong?

[EagleMark]

So far everything I've checked is only half... try this!

[JeepsAndGuns]

Tried that ADX and if it is correct, then I am going well over 100% DC when in PE and hammering on it. I saw the DC go up to 119.02% on a recored log when I was hammering on it. TPS 73%, MAP 90, 4000 RPM, and in PE. WB AFR was still at 12.6, so it wasnt going lean, but I cant speak for weather the injectors were going static.

Are you 100% sure it is displaying the correct DC %?

Exact same time data sample on the normal adx was 59.51% DC

[EagleMark]

Sorry, for got you were MPFI, change the 4 to a 2 in conversion.

TBI IDC (%) = [4 * IPW (ms) * RPM]/1200
MPFI IDC (%) = [2 * IPW (ms) * RPM]/1200

[JeepsAndGuns]

Sorry, for got you were MPFI, change the 4 to a 2 in conversion.

TBI IDC (%) = [4 * IPW (ms) * RPM]/1200
MPFI IDC (%) = [2 * IPW (ms) * RPM]/1200

Ok, did that and it changed back to what it was before in the old ADX. Same time stamp data sample listed above, its 59.51%. So I'm guessing I'm good?

[EagleMark]

I'd say good and remember one of your logs at 61%.

So although different format it looks like the origanal was accurate for MPFI.

[CCFI]

http://wiki.openoffice.org/wiki/Documentation/How_Tos/Calc:_ROUND_function : It specifies number of places to ROUND, if you still care.

[devind]

I have read and reread this thread trying get a better understanding of the info needed to use the TBI calculator Mark created.
What is bsfc? And how do I know what the value is?
Also in the calculator it gives bpc.
If using the calculated values to tune a $42 tune is that the same as bpw?

[Six_Shooter]

BSFC = Brake Specific Fuel Consumption

For N/A engines this is generally between .45 and .50, Supercharged engines between .50 and .60 and turbocharged engines between .55 and .65.

[devind]

BSFC = Brake Specific Fuel Consumption

For N/A engines this is generally between .45 and .50, Supercharged engines between .50 and .60 and turbocharged engines between .55 and .65.

Thank You!!

[PJG1173]

(X*4*Y)/1200

X= BPW and Y=Engine RPM.

TBI IDC (%) = [4 * IPW (ms) * RPM]/1200

Wrong calculation was started here in 2007:
http://www.fullsizechevy.com/forum/general-discussion/performance/tbi-tuning-87-95-obd-i-ecm-pcm/297086-calculating-injector-duty-cycle-injector-pulse-width.html

Comes out correct to 1project2many TBI helper and all other math...

interesting... my ADX has X*Y/60000*100. when I change to the above I am seeing higher IDC's.

[EagleMark]

Right! The old way is actually 50% of IDC!

[Tbrendal]

I've got about a bazillion hours into learning spreadsheets. Almost 13 hours into edits in this one recorded in the file.

Special Thanks to Dave W at Old School EFI for sharing his BLM spreadsheets, they are all included.

For evaluation only! I've tested till I'm blind and it all seems to work properly. Warning, spreadsheet on steroids! If it passes inspection I think it's worthy of GearHead-EFI.com name...

EDIT: New upload with protection issue on Injector Duty Cycle fixed.

I tried using your calculator but the content does not work . For some reason I am losing all the formulas attached to the spreadsheet. Help!!!

[dave w]

I tried using your calculator but the content does not work . For some reason I am losing all the formulas attached to the spreadsheet. Help!!!
Tbrendal, It saddens me to tell you, EagleMark lost his battle with cancer and passed away just over a year ago.

I'll try helping you with spreadsheet. I need to know the post # of the spreadsheet you are using.

dave w

[Tbrendal]

Damn! I'm sorry to here that. I feel like I know the guy after reading all the work he has done here for us. Of course I guess it is nice to know his legacy lives on!!!

[Tbrendal]

It post # 18 of this thread.

[dave w]

It post # 18 of this thread.

The spreadsheet in post #18 is an Open Office .ods file: https://www.openoffice.org/ if you want to download and use freeware Open Office.

Post # 20 has a Microsoft Excel .xls file if you have Excel. I've also re-attached the file from Post #20, see below. I just tried using the attached .xls, seems to be working for me.

Please update me with your progress.

dave w

[Tbrendal]

Thanks Dave!. I didn't notice it wasn't an excell document.
First let me give you my specs.
I have a .030 350 block with the stock dish pistons, RV cam, Vortec heads with an air gap intake manifold. Im running the 5.7 throttle body that has all the ultimate mods done. 18 PSI spring and a 40 PSI in tank fuel pump. My truck runs the 7747 ECM. I started with an ASDU stock bin with the highway fuel added to it provided by Eagle Mark!
I did the math and have set my BPW to 104. I had a heck of a time before resetting that. My injectors were running at 100% duty cycle all the time. Once I put the 104 in the BPW it came down to where it should be. I will finally log some good data on the way home tonight! I also changed the ASDU stock BIN over to a Vortec head timing curve. Other than that I have not made any changes yet.

Sorry to hear about Eagle Mark again. That guy was quite the innovator !

[Tbrendal]

How do you copy the BLM table from a log on tunerpro? or do you have to enter all the values manually?

[dave w]

Are you using the running average from the TunerPro RT history tables?

Highlight the cells, then press down on both the Ctrl and "C" (Control C) on the keyboard to copy the averages. To paste, press down both Ctrl and "V" (Control V) on the keyboard.

dave w

[Tbrendal]

Ya I get that I was right clicking and trying to save. But it doesn't give me that option. There must be a setting in Tunerpro I don't have selected or something.

[Tbrendal]

SO thanks Dave for all the work with the TBI calculator and all the other stuff you guys have done for us. One quick question though. I have added my VE2 table to VE1 and tuned to get close. Once that is done should you put the VE2 table back to its initial settings?

[dave w]

Once the VE tuning is finished, no changes are needed to either VE1 or VE2.

dave w

[Tbrendal]

Thanks for your help Dave.

[350yj]

The spreadsheet in post #18 is an Open Office .ods file: https://www.openoffice.org/ if you want to download and use freeware Open Office.

Post # 20 has a Microsoft Excel .xls file if you have Excel. I've also re-attached the file from Post #20, see below. I just tried using the attached .xls, seems to be working for me.

Please update me with your progress.

dave w


Using this spreadsheet, running 100% duty cycle on my injectors indicates a supported horsepower of 306. I feel I have been wronged. I purchased a rebuilt TBI unit from SPR performance, specs below:

46mm TBI Kit
New TPS, New IAC, TPS adapter, 65lb flow-matched injectors, 18psi spring, thinned shaft, bushed shaft, 1/4" pod spacer, shaved air horns, adj reg cover, custom cut 46mm base gasket

I specified I was using a kit from Summit Racing (SME-K-355-400), link to cam specifics here (http://www.summitracing.com/int/parts/sum-1103). I'm considering selling all the GM TBI parts and going for an MPFI self learning kit from Fast.

--
Kris

[Tbrendal]

I am by no means an expert but running your injectors at 100% is not good. You need to increase your BPW

[350yj]

IIRC, this is a zero sum game; increasing the BPW or increasing the duty cycle from the injectors. Either way, the amount of time the injectors are firing is the same.

--
Kris

[dave w]

One of my 5.7 liter TBI tuned engines ('7427 PCM using a Wide Band O2 Sensor to tune with) went on a Dyno ... the results were 330 RWHP using 65 cop car injectors with a stock fuel pressure regulator spring and 670 CFM (50mm Throttle Body).

The FAST system might be an option. I would use a '7427 PCM in MPFI mode. Personally, I fell I can tune better than the self learning FAST system.:thumbsup:

dave w

[350yj]

Thanks for your reply Dave. I feel like I *could* tune better than a FAST or Holley MPFI system with enough time and trial and error. I have had this setup for over a year and not had the time to learn enough to make a perfectly drivable bin IMO. However, I feel as though there are some limitations to the 1227747 $42 ECM that can't be solved such as:

Inability to correct using a wide band
Low-resolution fuel/spark tables
Slow sensor polling intervals

The FAST or Holley MPFI kits are not cheap and do require standalone Ignition controls. Probably total parts cost of 4 grand. On the plus side, there is now a one to one relationship with the injector and cylinder. I would really like the current TBI system to run as smoothly as my daily driver but feel as though I am currently overwhelmed with tuning and have a need of my Jeep being ready for the winter.

Lastly, I feel as though the Holley or FAST kit would net me better fuel economy. Currently averaging 10 MPG with this setup in a 1990 Jeep Wrangler YJ which weighs in around 3300 pounds. I have the motor bolted up to the stock AX15 5 speed with a custom bellhousing, 4.10 gears and 35 inch tires. It will run around 2k RPM doing 70. The MPG isn't the problem so much so is the 15 gallon fuel tank. My commute into work is 80 miles round trip and having to fill up every day is annoying.

--
Kris

[1project2many]

The 7747 seems to have less functionality than later computers. It is somewhat harder to tune imo and I have not opted to use one in years. I plan to use a 7427 or 7730 when I put my 4.0 / AX15 combination together. There are ways to do all you want with a stock ecm but it takes some work and time to set up hardware and software. Just like trying to use a stock engine for a specific, high-performance purpose, the stock computer was built for stock applications and will require "help" if you want to extend its abilities.

It is more challenging to tune for maximum fuel economy than to "get it running." It takes time. You need to log a trip to work, pour over the trip, and look for areas where you can make improvements. Do the same on the trip home. Watch for conditions like high MAP causing the ecm to enter PE mode. Watch to see if you can lean out fuel and maintain power. Advance and retard timing in small increments at cruise to see if it makes a change in economy. It is the same approach as with a carburetor but with the advantage of being able to log conditions and view them later. Opting for another system means making another set of tradeoffs... I personally have not seen that the significant additional investment allows one to skip spending time with the system to get best results. Still, I also know that there is no rational approach which will trump what a person "feels" will work best. If your heart is set on spending money for a solution I'd ask, in all honesty, that you report on your experiences should you decide to switch systems. I would also advise looking at Dynamic EFI as an option. Bob Rauscher's system starts with a stock ecm like a 7747 but adds a considerable amount of functionality through custom code, additional hardware, and proprietary tuning.