injector size vs fuel pressure
Thread Starter
Melting Slicks
Joined: Sep 2001
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From: Dover De
Originally Posted by Nathan Plemons
If you don't have an adjustable fuel pressure regulator, basically you don't mess with it.
Original Founding Member!
Joined: Jul 1999
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From: Granby, MA
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kinda depends...
Originally Posted by emsrescu
I just put in the #24 ford svo injectors. what should i set the fuel pressure to? And how do i go about it? 
Jeff
Melting Slicks
Joined: Jan 2002
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From: Milan
The best thing to do is to change the Injector constant in your chip and let the pressure reulator as is.
Now (if stock) your chip injector constant is 22.07, you should change to about 26,4 (to compensate the different rate at wich the FMS injectors are rated at -43.5 vs. 39-).
Now (if stock) your chip injector constant is 22.07, you should change to about 26,4 (to compensate the different rate at wich the FMS injectors are rated at -43.5 vs. 39-).
Racer
Joined: Apr 2003
Posts: 286
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From: Suffolk VA
This site has some good math to explain how pressure effects mass flow of fuel through an injector...
http://www.rceng.com/technical.htm
Tuned Port Induction Specialties Inc. has a couple Books on the subject too.... www.tpis.com
http://www.rceng.com/technical.htm
Tuned Port Induction Specialties Inc. has a couple Books on the subject too.... www.tpis.com
Team Owner
Joined: Dec 2000
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From: SE NY
Cruise-In II Veteran
Fuel flow varies as the SQRT of the pressure ratio. Since the FMS are rated 24lb/hr @43.5psi and stocks were rated 22lb/hr @39psi they essentially flow the same at a given fuel pressure:
24lb/hr * SQRT(39/43.5) = 24lb/hr * 0.947 = 22.7lb/hr
That 3% increase in flow with the FMS shouldn't be a problem, so set fuel pressure to the stock value.
24lb/hr * SQRT(39/43.5) = 24lb/hr * 0.947 = 22.7lb/hr
That 3% increase in flow with the FMS shouldn't be a problem, so set fuel pressure to the stock value.
Racer
Joined: Apr 2002
Posts: 342
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From: new orleans La
Originally Posted by emsrescu
I just put in the #24 ford svo injectors. what should i set the fuel pressure to? And how do i go about it?
heres a cool site with some charts: http://paradox.shacknet.nu/dave88lx/.../injectors.htm
click on the bottom of the page where it says "fuel pressure"
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Melting Slicks
Joined: Jan 2002
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From: Milan
Originally Posted by 65Z01
Fuel flow varies as the SQRT of the pressure ratio. Since the FMS are rated 24lb/hr @43.5psi and stocks were rated 22lb/hr @39psi they essentially flow the same at a given fuel pressure:
24lb/hr * SQRT(39/43.5) = 24lb/hr * 0.947 = 22.7lb/hr
That 3% increase in flow with the FMS shouldn't be a problem, so set fuel pressure to the stock value.
24lb/hr * SQRT(39/43.5) = 24lb/hr * 0.947 = 22.7lb/hr
That 3% increase in flow with the FMS shouldn't be a problem, so set fuel pressure to the stock value.
Probably i contributed to create confusion with my post.
It seems that FORD injectors are rated (in this case 24 lb/h) at a LOWER pressure (near to 39 psi). and GM injectors are rated at HIGHER pressure (about 43 psi). So at the same pressure (say 43 psi) the FORD SVO ones flows a 10% more!
Is just the opposite you said in your post.
It's for this reason that installing SVO injectors you should put an HIGHER injector constant than advertised by SVO injectors (26 instead of 24). If you say to the ECM that you injector is bigger it stays open a bit less. If you do not change pressure, and you let the inj. constant to 22, the injector stays open the same time as before delivering MORE and MORE fuel.
...Then if the SVO injectors are REALLY rated at lower pressure (flow more at a given pressure compared to a GM one) is a mith or not I really don't know.
-Beppe-
Team Owner
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From: SE NY
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Ah, ok then the 24lb/hr FMS injectors would flow:
24lb/hr * SQRT(43.5/39) = 24lb/hr * 1.056 = 25.3lb/hr
To get 22lb/hr you will need to change the EPROM tables or lower fuel pressure to 35psi.
But the above is good info in case I do some real engine mods and need 25lb/hr injectors.
24lb/hr * SQRT(43.5/39) = 24lb/hr * 1.056 = 25.3lb/hr
To get 22lb/hr you will need to change the EPROM tables or lower fuel pressure to 35psi.
But the above is good info in case I do some real engine mods and need 25lb/hr injectors.