Fuel Pressure vs. Volume
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On The Tree
Joined: Jul 2002
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From: tampa fl.
Fuel Pressure vs. Volume I'm having a little fuel issue - was wondering if you can have plenty of pressure and not enough volume (fuel). The problem I'm having is that under full boost my car steadily ramps up to 85psi and does not drop, but my tuner said that the way he's having to add fuel it's like I'm running out of fuel. I have 2 255 fuel pumps on a boosta pump at 22volts @ 9psi ran to 1/2" line up to aeromotive fuel rails thru an aeromotive boost reference regulator and 3/8" back to the tank with 60psi injectors.
So, the question is -- are the 2 little pumps providing enough pressure but not enough volume. Would an aeromotive eliminator in-line fix the volume problem if there is one?
So, the question is -- are the 2 little pumps providing enough pressure but not enough volume. Would an aeromotive eliminator in-line fix the volume problem if there is one?
Sounds like you have plenty of fuel delivery if your
85PSI is at the rail. The tuner needs to look at the
injector duty cycle and see whether there is just
no more open-time left.
Also injector performance is affected by the line
pressure, increasing the opening delay time. 85PSI
against maybe 24PSI manifold is 60PSI working.
Don't know what the maximum head is, that the
injector will fail to open against. But at any rate
a high pressure has a higher offset value and it's
probably not modeled well (at all?) in the injector
offset table, and at high RPM your offset time
can be a large part of the total cycle?
85PSI is at the rail. The tuner needs to look at the
injector duty cycle and see whether there is just
no more open-time left.
Also injector performance is affected by the line
pressure, increasing the opening delay time. 85PSI
against maybe 24PSI manifold is 60PSI working.
Don't know what the maximum head is, that the
injector will fail to open against. But at any rate
a high pressure has a higher offset value and it's
probably not modeled well (at all?) in the injector
offset table, and at high RPM your offset time
can be a large part of the total cycle?
yea, jimmyblue is as always on the money.
i wrote a little program that allows you to play with pulse widths, opening/closing times, and the the window of time to inject fuel, check it out:
http://redhardsupra.blogspot.com/200...se-widths.html
i wrote a little program that allows you to play with pulse widths, opening/closing times, and the the window of time to inject fuel, check it out:
http://redhardsupra.blogspot.com/200...se-widths.html
My $.02..
Originally Posted by 01Bird_of_Prey
I'm having a little fuel issue - was wondering if you can have plenty of pressure and not enough volume (fuel). The problem I'm having is that under full boost my car steadily ramps up to 85psi and does not drop, but my tuner said that the way he's having to add fuel it's like I'm running out of fuel. I have 2 255 fuel pumps on a boosta pump at 22volts @ 9psi ran to 1/2" line up to aeromotive fuel rails thru an aeromotive boost reference regulator and 3/8" back to the tank with 60psi injectors.
So, the question is -- are the 2 little pumps providing enough pressure but not enough volume. Would an aeromotive eliminator in-line fix the volume problem if there is one?
So, the question is -- are the 2 little pumps providing enough pressure but not enough volume. Would an aeromotive eliminator in-line fix the volume problem if there is one?
At 800FWHP, BSFC of .6, duty cycle at 90%, equates to 67PPH injs..
Slamming them w/ 22VDC, is questionable, and could be affecting thier reliability.
If the PSI does not fall, but rises w/ boost, then the pumps are not being "outrun"..yet.
At that HP level, I'd be looking at:
A. 83# injs.
B. Return line at -8. A test for return line capacity: Attempt to turn the FP down 5# below the desired setting. If it goes, then the return is handling the flow. If it won't then it's time for more return capacity.[When checking, be sure pumps are at max voltage.]
Back under my rock...
I've not..
Originally Posted by 01Bird_of_Prey
Can get 83 psi injs hi or do i need low impedance?
Others may have more up to date info/source[s]??
