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Old 11-09-2004, 05:40   #1 (permalink)
Mcccli
 
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Increasing Fuel Pressure to Increase Injector Flow

After coming to realise the cost of an aftermarket ECU and larger injectors, Ive decided that I'll utilise what I've got (with a turbo set up) for the moment. I'm considering using the Vortech Super FMU (adjustable rising rate regulator for those unaware), or possibly one of their fixed rising rate regulators.
Anyways, after LOTS of reading, Ive found the following formula:
the square root of (New Fuel Pressure/Old Fuel Pressure [in PSI] )* original injector flow (cc/min)

I have heard that anything more than around 75PSI through the stock injectors is NO good because:
1) The spray pattern gets completely screwed, therefore causing an inefficient explosion of the air/fuel mixture
2) The pressure becomes too high so the solenoid, or whatever it is, cant open against the pressure of the fuel. (Perhaps thats why WRX use "side-fed" injectors??
Anyway, does anybody know what the limit of the stock injectors are?? (Think turbotrana said they were around 200cc/min)
This means that if I run a rising rate regulator, and increase the OVERALL fuel pressure to around 80PSI (I'm assuming stock its 33PSI at a guess), then I could increase the flow of my injectors to just under 320cc (or I think just over 45KW each), allowing (theoretically) up to 270kw.
So, IF 80PSI is the maximum pressure injectors can handle, if I chose to run UP TO 10PSI through my turbo, I would set the rising rate to about 5:1 (ie. for every pound of boost, the fuel pressure increases by 5PSI).

All this of course, depends IF 80PSI is the limit.
Anybody know about the injectors limits?
(PS Sorry, bout the long post for those of you who don't like to read, but this information took me a few hours to find and understand)
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Old 11-09-2004, 06:21   #2 (permalink)
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Re: Increasing Fuel Pressure to Increase Injector Flow

ive read pushing stock-type injectors past 58psi will dramatically shorten injector life. and at over 75 psi injector contol could be lost, also goes on to say that very few high flow injectors record any flow increase over 60psi, and smaller injectors often show no increase or not more than a gain of 2-3%, when the fuel pressure is raised from 4.1bar to 4.8bar (~61.5psi to ~72psi) because the injector takes much longer to open as the pressure increases.

its also got a chart of injector flow rates at different pressures- need the bosch part no. though, anyone know?
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Old 11-09-2004, 16:46   #3 (permalink)
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Re: Increasing Fuel Pressure to Increase Injector Flow

Was that an autospeed article??
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Old 11-10-2004, 01:30   #4 (permalink)
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Re: Increasing Fuel Pressure to Increase Injector Flow

nah, a book
"FORCED INDUCTIONS: Performance tuning", A. GRAHAM BELL, haynes publishing

it cost $70 but was well worth it
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Old 11-10-2004, 02:14   #5 (permalink)
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Re: Increasing Fuel Pressure to Increase Injector Flow

This is what I have been told and it worked for me. Firstly, the regulator rate is matched to injector size. Stock I6 injecotrs should run around an 8:1 regulator. Max fuel line pressure is around 90psi which menas you can run about 12psi boost with an 8:1 reg (8x12=96psi but then you take about 10-15psi off that for fuel pump losses etc so that means a fuel pressure of 80-90psi). Yes injector life does go down but that is mainly in regard to setting base fuel pressures high. because the rising rate regs only really kick in above 5psi, in normal driving you may never have anything more than stock fp. The fp will only reach 80-90psi on full boost runs and even then it is normally only for a short time. I know one falcon running a 12:1 reg with 8psi of boost and the injectors have done fine for over 100,000kms.

mcccy005 I sent you some more info by PM
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Old 11-10-2004, 04:38   #6 (permalink)
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Re: Increasing Fuel Pressure to Increase Injector Flow

In reply to what you said regarding the the fuel pressure, the fuel pressure in the line (stock) is already around 30-35PSI; so if you add 12PSI of boost, then at 8:1 fuel pressure, there will be around 115PSI (after taking out what you said as pressure losses) going through the injectors right? So if thats true, I would only be able to run about 8 PSI on the 8:1 regulator?? (8PSI*8:1fuel = 64PSI + the 30PSI already in the line??)
Anyway, that was my understanding and I havent actually spoken to anybody about this as yet - just what I've read around the place
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Old 11-10-2004, 04:49   #7 (permalink)
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Re: Increasing Fuel Pressure to Increase Injector Flow

Quote:
Originally Posted by mcccy005
In reply to what you said regarding the the fuel pressure, the fuel pressure in the line (stock) is already around 30-35PSI; so if you add 12PSI of boost, then at 8:1 fuel pressure, there will be around 115PSI (after taking out what you said as pressure losses) going through the injectors right? So if thats true, I would only be able to run about 8 PSI on the 8:1 regulator?? (8PSI*8:1fuel = 64PSI + the 30PSI already in the line??)
Anyway, that was my understanding and I havent actually spoken to anybody about this as yet - just what I've read around the place
I explained it a little better in the PM I sent you. The rising rate reg actually start at 0psi and work their way up with boost. Anything under the stock fuel reg pressure (about 38psi I believe) the rising rate reg will have no effect. ie before 4-5psi of boost, the stock reg is in control, after that, the rising rate pressure is higher so that takes control.

But as I said, the regulator rate is really determined by the injector size. The max boost you can run is then determined depending on how high you want to push the fuel pressure. I was told 90psi is ok but not to go much higher than that.
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Old 11-10-2004, 05:00   #8 (permalink)
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Re: Increasing Fuel Pressure to Increase Injector Flow

Yep, I totally understand now.
Thanks
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