Fuel Injector Rates

[12_Square]

My injectors are rated by Bosch: 187g/min @ 300kPa. I want to set my injector flow rates correctly. {GM.MANVAC} I’m assuming that 187/60seconds = 3.11 grams per second, though I’ve seen conflicting data concerning g/sec with these injectors. (Somewhere I read they are 3.60g/sec, but at the same time 187g/min…)

I have a 98 LS1. Would I be correct in measuring my fuel rail pressure with the engine running? (I have not done this yet.)

IF rail pressure in my car is 344kPa, should I convert the injector rate 3.11g/sec @ 300kPa, to 3.56g/sec @ 344kPa and then use this equation to set my injector flow rate per vacuum:

Sqrt (344 + Manifold Vacuum / 344) x 3.56 = injector flow rate.

Example at 30kPa manifold vacuum:

Sqrt (344+30/344) x 3.56 = 3.71

Or with significant figures only:
344+30 = 374
374/344 = 1.09
Square Root of 1.09 = 1.04
1.04 x 3.56 = 3.70

Thus, 3.70g/sec @ 30kPa Manifold Vacuum?
My table has 3.7500 @ 30kPa from the factory.

[joecar]

You have to find out if your injectors are 3.11 g/s or 3.60 g/s... where are they from...?

Yes, measure rail pressure with engine running, should be 58 psi (400 kPa), see Service Manual for 1998 Y-car or 1998 F-car.


When I do the math it comes out like this (if your rail pressure is 344 kPa):

sqrt( 344 /300)*3.11 = 3.33 g/s at 344 kPa


then (with manvac in kPa):

IFR(manvac) = sqrt(( 344 +manvac)/344) *3.33

so (rounding to 2 decimal places):

IFR(0) = 3.33 g/s
IFR(5) = 3.35 g/s
IFR(10) = 3.37 g/s
. . .
IFR(30) = 3.47 g/s
. . .
IFR(80) = 3.70 g/s



Of course, instead of using 344 kPa, you would be using measured rail pressure (in three places), which for LS1 should be 400 kPa...

if your rail pressure is not 58 psi (400 kPa) then there exists a problem with your fuel pump/regulator/filter/plumbing (but having said all that, I have failed to ask what vehicle you have).

[joecar]

Measure your rail pressure, and redo your math, and post again.

Also, post a copy of your B4001 IFR table.

[joecar]

Looks like you have the stock 1998 Corvette/Camaro/Firebird IFR table.

[12_Square]

Okay, I have another variable here... I checked my fuel pressure. Initial pump prime makes the pressure jump to 64psi, then the line holds steady at 50psi (engine off.) With engine running it's steady at 64psi. Car has a 255lpg Walbro fuel pump and has been running with the stock '98 IFR table. The new injectors I'm working with now are 187g/min at 300kPa as rated by Bosch.

55 to 60psi is what the genuine GM manual specifies, but can I make it all work with the current pump, or is it better to buy a new one within the OEM range? (Or is there something wrong with the aftermarket one?) I do not run any kind of boost and never will on this car.

[12_Square]

So in theory:

187g/min / 60seconds/min = 3.116g/sec (Is that safe to assume with fuel injectors?)
64psi = 441kPa

3.116g/sec @ 300kPa with 441kPa rail pressure would be:

Sqrt (441kPa / 300kPa) x 3.116 = 3.778g/second

Then, fuel rate for manifold vacuum 5, etc
Sqrt (441+5 / 441) x 3.778 = 3.799

[joecar]

Okay, I have another variable here... I checked my fuel pressure. Initial pump prime makes the pressure jump to 64psi, then the line holds steady at 50psi (engine off.) With engine running it's steady at 64psi. Car has a 255lpg Walbro fuel pump and has been running with the stock '98 IFR table. The new injectors I'm working with now are 187g/min at 300kPa as rated by Bosch.

55 to 60psi is what the genuine GM manual specifies, but can I make it all work with the current pump, or is it better to buy a new one within the OEM range? (Or is there something wrong with the aftermarket one?) I do not run any kind of boost and never will on this car.

Ok, use 64 psi (441 kPa) as rail pressure, and use 187/60 = 3.12 g/s @ 300 kPa as the injector rating, and use the math to create an IFR, as you have done in post #6...

[joecar]

So in theory:

187g/min / 60seconds/min = 3.116g/sec (Is that safe to assume with fuel injectors?)
64psi = 441kPa

3.116g/sec @ 300kPa with 441kPa rail pressure would be:

Sqrt (441kPa / 300kPa) x 3.116 = 3.778g/second

Then, fuel rate for manifold vacuum 5, etc
Sqrt ((441+5) / 441) x 3.778 = 3.799

Yes, correct (parentheses added).

[12_Square]

Awesome. Thank you. It's tough to find the right kind of math on the internet!