Fpr setting for 550cc injectors.

[Stainbox12]

I bought a fuel pressure regulator which rises 1:1. Now, i know this is not a way to control injectors, and its actually used to lower the fuel pressure when a larger pump is installed, and caussing overrun. I recently sold my safc, and have no way to control my 550cc injectors, in theory, im running rich. Is there any setting on the fpr i can use with my 550cc, and not to run rich? I know, the base pressure of a 1g, is 37.5 psi, but since i don't have any way to control the bigger injectors, is there any way, i can lower the fuel pressure to make work the 550cc, and behave like or nearly stock, without high IDC's? In other words, can i tune until i get new management with my fpr? Thanks.

 

[spectr019]

uuum I would say no? If we could tune with only an fuel pressure regulator, there would be no need for other fancy devices, such as the afc...So yeah I would think the answer would be no, get your afc back or something quick cause your throwing in approximately 18% more fuel for stock settings. What pump are you using?

Ben

 

[matthewdesigns]

Not really the best thing to do, but...

Your best bet is probably to try to set your fuel trims to normal using your fpr. Log your LTFTs on a nice, long cruise at about 55mph, and try to get those stabilized by reducing your fuel pressure a little at a time, until you get back to normal. I wouldn't go more than a few psi, though, as you might run into other issues. That will at least get you closer to a stoich "tune" in open loop operation, but might make you susceptible to a leaner condition at WOT, so I wouldn't go jumping on the throttle unless you have a WBo2 setup to keep an eye on things.

 

[1992awdlaser]

In order to get them close to what the stock injectors flow at 37.5psi fuel pressure, you would need to lower the fuel pressure to about 25psi.

 

[No_Skillz]

Old Injectors / New Injectors / Fuel Pressure Ratio - 1 = Injector Adjustments

Injector Adjustments are 0 due to your lack of tuning devices so we have:

450 / 550 / Ratio - 1 = 0
Ratio = 0.8181

Then,

Fuel Pressure Ratio = New Pressure / Old Pressure
0.8181 = New Pressure / 43.5
New Pressure = 35.59

You are shooting for 35.6 with vacuum hose off, 26.6 with vacuum hose on.

 

[Splitpi]

New Injector Flow = SQRT(New Pressure/ Old Pressure) * Old Flow

Solving:

450 = SQRT( X / 37.5) * 550
0.818182 = SQRT ( X / 37.5)
0.669421 = X / 37.5
X = 25.1 psi

So a new base fuel pressure of 25.1 psi would make the 550's flow like 450's. Assuming Dead Time is the same, the ECU would not know the difference.

1992awdlaser was correct.

 

[1992awdlaser]

Old Injectors / New Injectors / Fuel Pressure Ratio - 1 = Injector Adjustments

Injector Adjustments are 0 due to your lack of tuning devices so we have:

450 / 550 / Ratio - 1 = 0
Ratio = 0.8181

Then,

Fuel Pressure Ratio = New Pressure / Old Pressure
0.8181 = New Pressure / 43.5
New Pressure = 35.59

You are shooting for 35.6 with vacuum hose off, 26.6 with vacuum hose on.

What?

Fuel injector flow if pressure is not 43.5psi
1g auto fuel pressure=43.5psi
1g manual fuel presure=37.5psi
SQRT(new pressure/old pressure) * old flow rate

Stock injector actual flow
SQRT(37.5/43.5) * 450 = 411.08 cc/min

550cc injector flow at 25psi
SQRT(25/43.5)*550=416.95cc/min

Or

SQRT(24/43.5)*550=408.52cc/min


At 35.6psi the 550's would be flowing:
SQRT(36.5/43.5)*550=497.55cc/min

 

[Stainbox12]

Alright im getting it. I actually did the same math and came around 25 psi of fuel pressure. And its interesting that you can actually can get close to stock while cruising but might have problems at WOT, so i guess that besides going 25 psi, i should bump it up a little bit more to be on the safe side (rich). I remember the old days when people really used FPR's to tune cars, maybe not to perfection but it did the job without all this new fancy devices.

 

[Splitpi]

Don't forget about Injector Dead Time, this will effect the speed at which the injectors can by cycled on and off. And if the ECU thinks they are faster than they really are... you may run lean.

Also you cannot tune out dead time via just the FPR as the air density due to humidity, temperature extra will effect the flow amount needed and this will very the required fuel amount calculated by the ECU. You can get close mind you.... but the best method is to tune via the ECU for dead time.

Here's a decent write up on Dead Time explanation:
Yaw Power Products / Injector Dead Times Explained

 

[No_Skillz]

What?

At 35.6psi the 550's would be flowing:
SQRT(36.5/43.5)*550=497.55cc/min

35.6/43.5*550=450.11

Think your typo messed you up a bit. However, I did overlook the fact that he is a 1g at 37.5psi. My bad.

BUT:
X/37.5*550=450
X=30.68psi

What is the SQRT that is factored into the equations?

 

[Splitpi]

What is the SQRT that is factored into the equations?

Its not a linear correlation. The flow rate increases by the square root of the pressure change ratio.

Here's a decent read on the subject:
How to Tune and Modify Engine ... - Google Book Search

And if you really wanted to solve the math... you can break out your fluid dynamics book and look up "Orifice Plate" and "Compressible Flow" for some help and then reduce to find the new flow rate based upon pressure changes. I have no desire to solve it here though. But I know the difference is non-linear and the flow rate increases by the square root of the pressure change ratio.

 

[No_Skillz]

Ooooohhhh...

Cool. I learned something today.

 

[1992awdlaser]

35.6/43.5*550=450.11

Think your typo messed you up a bit. However, I did overlook the fact that he is a 1g at 37.5psi. My bad.

BUT:
X/37.5*550=450
X=30.68psi

What is the SQRT that is factored into the equations?

Yeah the typo did mess it up a little. This is what it would really be:

SQRT(37.5/43.5)*550=510.66cc/min

It's sttil the same that it should be set at 25psi to flow what the 450's flow at 37.5psi.

 

[Splitpi]

It's sttil the same that it should be set at 25psi to flow what the 450's flow at 37.5psi.

It didn't affect the final outcome because both injectors are rated at 43 psi. I.e. the 450's flow 450 cc/min @ 43 psi @ 100% IDC and the 550's flow 550 cc/min @ 43 psi @ 100% IDC. Thus all things being equal (pressure and IDC) we didn't need to correct the values being used.

 

[1992awdlaser]

It didn't affect the final outcome because both injectors are rated at 43 psi. I.e. the 450's flow 450 cc/min @ 43 psi @ 100% IDC and the 550's flow 550 cc/min @ 43 psi @ 100% IDC. Thus all things being equal (pressure and IDC) we didn't need to correct the values being used.

I was saying for that equation, the number the 550's would flow at stock pressure was off since I used a lower than stock fuel pressure. I know it had nothing to do with the final outcome of what the pressure should be set at.

 

[flinguist]

What?

Fuel injector flow if pressure is not 43.5psi
1g auto fuel pressure=43.5psi
1g manual fuel presure=37.5psi
SQRT(new pressure/old pressure) * old flow rate

Stock injector actual flow
SQRT(37.5/43.5) * 450 = 411.08 cc/min

550cc injector flow at 25psi
SQRT(25/43.5)*550=416.95cc/min

Or

SQRT(24/43.5)*550=408.52cc/min




At 35.6psi the 550's would be flowing:
SQRT(36.5/43.5)*550=497.55cc/min

Don't forget that 1G auto injectors are 390cc/min..