Injectors Injectors Injectors.....

[DeWynter]

I want to upgrade my injectors and thought it would be ok to use a set of 28.6 # C5 LS1 injectos rated at 4 bar pressure, but my question is are the flow ratres linear? Eg. 28.6@58(4 bar) = 21.45@43.5(3 bar) or are they non linear eg. 28.6@58(4 bar) = 24ish@43.5(3 bar) If they are linear I will just adjust my FP to make them 24 # but I want to have a pretty close measurment at pressure as I dont want to have to screw around endlessly with the FP to tune the engine. By linear calcs, to get a 25 # injector I would have to produce a 50 PSI fuel system, Which I believe is possible on a TPI as I have herd of people in the 55 PSI area.

[fastTa]

I want to upgrade my injectors and thought it would be ok to use a set of 28.6 # C5 LS1 injectos rated at 4 bar pressure, but my question is are the flow ratres linear? Eg. 28.6@58(4 bar) = 21.45@43.5(3 bar) or are they non linear eg. 28.6@58(4 bar) = 24ish@43.5(3 bar) If they are linear I will just adjust my FP to make them 24 # but I want to have a pretty close measurment at pressure as I dont want to have to screw around endlessly with the FP to tune the engine. By linear calcs, to get a 25 # injector I would have to produce a 50 PSI fuel system, Which I believe is possible on a TPI as I have herd of people in the 55 PSI area.

I'm kinda tired of typing today.

So here are two links that I think you will find very useful:

Essentially yes, pintle type injectors are basically linear up until a certain point dictated by their MLPT and DFR and/or in excess of 85%-90% duty cycle.

http://www.tagelectronics.co.uk/Prod.../Injectors.asp

http://www.chevythunder.com/fuel%20i...ance%20pg2.htm

[Injuneer]

Not sure, but I think the question he asked was whether the change in flow is "linear" with respect to pressure. The answer is "no". The flow changes with the square root of the pressure ratio.... in effect, an injector rated at 28.6#/Hr at 58psi (4bar) will only flow 24.77 #/HR at 43.5psi (3bar). The stock LT1 injectors are programmed as 24.896 #/HR in the PCM.

How the LS1 injectors are rated has been a roller coaster.... the references I saw indicated that they were flow rated at the LS1 fuel system operating pressure of 4bar. Then I think it was Racetronix who indicated that they were actually rated at 3bar.... but lately, SLP and Racetronix seem to agree that the LS1's are flow rated at 4bar, and will only flow 86.6% of that rating when run at 3bar.

The math:

28.6 X (43.5 / 58 )^0.5 = 28.6 x ( 0.75 )^0.5 = 28.6 X 0.866 = 24.77

The flow capacity entered into the program is just part of the input. The PCM also needs the "offsets" to understand how fast the injector opens and closes as a function of system voltage.

I think I would use a slightly larger injector, or a higher fuel pressure, based on your 356rwHP number. The larger injector keeps the duty cycle under control, and leaves you room for future power increases. There is no "downside" to a larger injector, as long as you don't get ridiculous and end up with an injector that can't be turned down to a low enough pulse width to get the engine to idle. But a 30# injector (rated/operated at 3bar) would be fine for your application.

[fastTa]

My mind was still on azkkn's question about rising rate FPR's. So I was still thinking in terms of the FPR - MAP relationship.

Yes, as far as the sustained differential fuel pressure vs. injector flow rate, it is increased in proportion to the square root of the measured sustained differential fuel pressure.

A 30lb/hr injector would be more than sufficient for your application. I ran the 30lb SVO's in my TA at 488 RWHP with a max measured duty cycle of ~78%.

Here is another good link to read some more about the TBI EPROM and its functions.

http://www.fuelinjection.com/portinj.html

Not exactly sure about the EPROM chip in your TBI, but with the LT1's you can edit the following fuel related PCM functions:

Fuel Air Ratio Table
Volumetric Efficiency Table
MAF calibration Table
Fuel Pressure versus voltage
Fuel Injector flow rate Manifold vacuum
Fuel injector Offset Table
Power Enrichment vs Temp Table
Power enrichment versus RPM Table
Wide Open Throttle Hot & Cold Tables
Closed Loop Enable vs Temperature

An interesting thing to note about the "Fuel Pressure vs. Voltage" setting is that as the MAP tells the FPR to hold additional pressure in the rail, the fuel pump is placed under a greater load. Normally a fuel pump provides greater flow through the supply line by means of more voltage and hence a higher motor speed. Well, when the fuel pressure rises and the pump sees a greater load the motor will actaully slow down and place the pump under a greater electrical load as well.

Make sure you are getting at least 11.5 volts as close as you can get a reading to the hot wire for the pump. 12 volts or more would be idel.

[fastTa]

Interesting graph:

[Racetronix]

I want to upgrade my injectors and thought it would be ok to use a set of 28.6 # C5 LS1 injectos rated at 4 bar pressure, but my question is are the flow ratres linear? Eg. 28.6@58(4 bar) = 21.45@43.5(3 bar) or are they non linear eg. 28.6@58(4 bar) = 24ish@43.5(3 bar) If they are linear I will just adjust my FP to make them 24 # but I want to have a pretty close measurment at pressure as I dont want to have to screw around endlessly with the FP to tune the engine. By linear calcs, to get a 25 # injector I would have to produce a 50 PSI fuel system, Which I believe is possible on a TPI as I have herd of people in the 55 PSI area.

Perhaps you should consider these:
http://www.racetronix.com/621020.html