BPW and Injector math

[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).

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?

[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.

[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.