what does the injector contant do and what are benifits from changing it. also i couldn't find it in my chip but i found BPW contant. is that it. its a 91 rs tbi 8746.

 

i dont see any benefit in changing it. the benefit is placing in constants, at a correct fiqure, in tuning program. If I recall it is based upon engine size, fuel pressure , and injector size. somewhere is a formula. once you set it forget it. I have a formula somewhere at home. can look up if you need it...

 

In your application it is BPW, not an injector constant.
You need to change it when you change to a different size injector, or you run out of range in the VE table to account for the difference in size.

 

well what should it be for 55 pound injectors. and on wednesday im moving to 85lbs.

 

what is the fuel pressure to injector?

 

right now im running like 16 to the 55lbs.

 

BPW Constant = 1461.5 X engine size in Liters / # of cylinders/ injector flow rate in gms /sec

convert injector flow from lbs/hr to gms/sec or 453.6 grams/ lb

now the formula to adjust for FP is the injector size in gms/sec times the square root of (current fuel pressure/GM fuel pressure)

 

Ok, I'm working with the 1227747 and using the 7747-mine.ecu file I have located:

Minimum BPW Hyst Value
Minimum BPW
Injector bias (added)
Max Async BPW
Min Async BPW

All of these have values way bigger than what the formula above calculates. Is one of these THE injector constant that needs to be changed when swapping injectors or is it hiding somewhere else?

 

HHmmmm. I use tunercat with a speed density TBI system. my injectors(2) are rated 90 lbs. In TC in constants is a BPW Constant that i am running at 93 however the above formula shows 107 due to my lower FP(9) than 12 lbs(GM specs). i may change it to 107 but that means i need to revisit all my entries for past 60 days. maybe someone else can explain what you are seeing????

 

Does tuner cat give you the Hex address of that constant?

 

Can you shorten-up or handle your apparent sig properly? I say apparent because a sig is only supposed to be displayed in your first post of the thread. Yours is visable in every post you make. Two lines in the post then 30 lines of sig, makes me skip the thread. . .

Thanks,

RBob.

 

Nevermind... I pulled my head out of the warm, dark, smelly place it was in realized I had skipped right over it in the list.

 

Will do.

 

Hex address? I dont think so. to get that i think one would email them. they respond to my emails within 24 hours. you can try the TC program free for 30 days!

 

i am way lost with that formula. i got something way off i think. less than 1

right now my injector constant is at 135. i have a 357 lo5. what should i put it to for the 65 pound injectors.

 

;* Val = 1461.5 * (VOL/RATE)
;* VOL = Vol of 1 Cylinder in liters
;* RATE = Injector flow in gms/sec


357 ci: 357 * 16.39 = 5851 cc's

5.851l / 8 = 0.73140375 l/cyl

65 #/hr: 65 / 3600 * 453.6 = 8.19 gm/s

BPC = 1461.5 * (0.73140375 / 8.19) = 130.5 or 131

The hex address of the BPC in a '747 is $2B4

RBob.

 

so the bigger the injectors, the smaller the BPW should be. because on my stock chip (305) its at 134. and the stock caprice chip (350) is 135. so now i should move to 131. that doesn't seem right, unless it has to do wiht me having non stock fuel pressure at 15psi

 

It is a ratio of displacement vs. injector flow. If your BPC is currently at 135 and the VE tables are coming together, leave it where it is.

RBob.

 

well i think right now i cant seem to get it richer in some areas. but today im switchin to 65lb from 55. so i wanted to know where i should put it.

 

Old post but I thought using it would be as good as starting a new one.

Question on the math. A 350 with 350 injectors is set at 135 and a 305 with 305 injectors is set at 148. What would it need to be set at if 350 injectors are used on a 305?

I tried the formula and I am wondering if someone could do it to to check my number against.

Thanks

 

I use 120, works out OK. This is with the ORG/BLK 350 injectors with a stock FPR.

RBob.

 

Thanks, I come up with 118 so it looks like I am on track here.

 

The AE has ended up rich on everything I have tuned so far, when I just change the BPWC and the VE tables. You have to really sit down and find out what the AE and Decel Enleanment need to be. Otherwise my engines have seemed to run a little rough and dirty. Also need to more than likely change values for the IAC pumpshot which gives fuel when the IAC opens, like when your A/C kicks in. Cold start will also give you some troubles occasionally as well.