Heres a hypothetical situation on say a 730 or a 746, 747, whatever (an ecm with a BPW constant)

Lets say its at wot, 100kpa at an rpm where the VE cell is at 100%
and lets say we have X (just a given number) for the bpw constant

then, all else exactly the same, (every other variable) we change the injector constant to Y ( a lower number)

What would happen to the injector pulsewidth? Increase? decrease? stay the same?

Oh yeah, I should have warned you.. this might sound like a dumb question.

 

Lowering the BPC will decrease the PW.

RBob.

 

RBob

How many calibrations for 730s use a BPW constant? I haven't seen "all" the 7730 calibrations, but the few that I've seen for V8s and V6s seem to use an "Injector Flow Rate" where you enter the Lbs. / Hr. Decreasing the Flow Rate constant (with no further changes to the vehicle or BIN) richens the mixture and increasing the Flow Rate leans the mixture.

I just want to clarify so a "newbie" SD TPI car knows that your answer doesn't apply to him and they should use what I just described above.

 

$88 (f-body v6), $A1 (FWD stuff) are two that I know of. Supposedly ~ 28 maskid's for the '730.

RBob.

 

Ok, thats what I figured. I asked to be sure I wasnt over looking something

Heres a follow up question

Lets say I have a TBI engine with the stock injector size and stock bpw with the same situation as above, 100% ve at a given cell in WOT but the engine is not stock and is still going lean in that area. Meanwhile, we leave the PE AFR table alone and its at 12.7:1

I then decide to install larger injectors
A quick look at the hack and I find this

So I adjust the BPW accordingly to a lower number


question: Would I, or would I not be just as lean as I was before in that same area despite the larger injectors?

 

Bttt

 

I have:
01
3E
46
51
55
6B
6D
88
89
8D
A1
D8,
as being for the 730.

 

Pablo, I think you are correct. BUT, since the flow characteristics of an injector are not completely linear, some adjustment to the VE table must be done after you change the BPC.

I was maxing out my VE tables with my 350. I raised the fuel pressure to 20 psi with 55 lb/hr injectors. I did not adjust the BPC, because I needed more "room" to work with in the VE tables. So I turned the VE#2 table (7747 ECM here) down 33 clicks. That compensated for the fuel pressure rise and fixed my maxed VE table problem.

Most of the values in the VE#2 table were 100. I took 13 psi / 20 psi and got .65. So I took .65 x 100 and got 65. This was just an estimate, after some tuning I arrived at 67's in the VE#2 table.

 

Why are you running so much in the number 2 table? What is the last line (3200rpm) max value in the first/main table? I hope it isn't more than 33 else we've gotta talk.
Just a FYI, to compensate for fuel pressure you don't just devide, a better guestimation would be to take the square root of old pressure divided by new pressure, then multiply.

Pablo, I know what you're thinking and I figured it out a while ago, never got around to telling you. By telling the ecm what sized injectors you've got you'll only run out of fuel IF you are seeing more than 100%VE or so it would seem. I cranked my fuel pressure all the way up to 28psi and I love it. I went from an injector constant of 135 down to 100 at the same time. I'm REALLY confused as to what size these holley injectors are (and at what psi they were tested at) so I took a stab at it. Anyways, my BLMs are dead nutz between 125 and 130 first time out. I also completely revamped my VE and timing tables according to some cheap and then expensive software (desktop dyno 2000 and virtual 4-stroke).
If I were in your position I'd crank the pressure up at least 20psi and from there set your injector constant to something like 110. You won't be hurting injector on-times by decreasing the injector constant. Or at least I don't think you would. Simply because the computer doesn't care what size injector you've got, it just looks at vol eff. You'd be suprised how accurate desktop dyno is if you know how to average out the blunders. Hint; average out the single plane table values with the dual plane if you've got an RPM manifold, I know you've got a torker so ignore that.....then average the high performance manifolds with the small tubes with mufflers if you've got headers. With the output of the VE and correct injector constant I'll be you'll be very close. BTW, DD2000 only does the vol eff for 100kpa (WOT) so you'll need to "shape" the fuel curve understanding that at peak torque on your motor will be the peak vol eff and anything less than 100kpa will also require less fuel. I'd just bell shape the curve and take out a bunch of fuel for idle if you run high pressure. You might need to adjust the pumpshot tables and pretty much start over but it's worth a shot. Oh yeah, be certain you've got good flow numbers for your heads or else this trick might not even work worth a damn.

 

That's the way the cal was when I started. The ASDU cal already had more than 100% in the tables. When I say the VE#2 was 100 I meant that it was unconverted. I'm using WinBin and I like looking at the VE tables unconverted, easier to see the "slope" of everything when I'm not staring at decimal points. After this change, the sum of both tables did not exceed 255.

 

You know I knew about the DD2000 trick way back. I actually did it with my car back when I first started and I remember the car running ***** to the wall with it but I didnt think it could be right even though I didnt do any testing so I ended up going another route which didnt work so well.

Anyhow im not quite sure I understand what you mean about the bpw and whatnot.. Basically my question comes down to if whether the ve% means anything at all once you go to a non stock injector size for your application or put another way, if that formula is worth a damn when it comes to calculating BPW. What would be the sense in just getting back to where you started even though you put larger injectors in if you were to adjust the bpw like that.

 

From what I've done...no. I've tried different injector/fuel pressure/BPC/VE table combinations. You can arrive at the same point with every different combination (within reason) depending on how you tune it.

I was maxing out my VE tables. So I turned the fuel pressure to 20 psi. I compensate I could've done 2 things: turned the BPC down, or turn the VE tables down. Since I was maxing out the VE I tables I turned those down. I figure my injectors were flowing 68 pph at 20 psi. If you put that thru the BPC formula it would yield a BPC of 121.5. BUT I had it at 133 and compensated in the VE tables.

I did this so I could have some room to tune. I was still lean at the top end with the maxed VE tables, and I didn't like the idea of "band aid fixing" it with PE mode.