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Discussion Starter #1
please help me settle this argument between me and my girlfriend - she says that my fuel pressure rises as rpms rise, specifically when I'm driving like a maniac. I think that, as the fuel pump is electric, that fuel pressure is constant, and if anything, drops a little when the injectors are at higher duty percentages.



am I right?
 

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Discussion Starter #3
RB26 engine, both turbos working (knocks on wood)
 

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If you have a progressive fuelpressure regulator then the fuelpressure will rise with boost pressure.

If it is a 1:1 regulator, you will have one pressure with vacuum, and one with boost.

Asim...
 

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The fuel pressure is kept constant over the injectors, therefore it changes with manifold vacuum / boost.

EG about 2.4 bar at idle will give you maybe 3 bar at 0 manifold pressure, and 4 bar at 1 bar of boost. It doesn't have anything to do with revs, or if you car is turbo or not - the regulator always keeps a constant pressure differential across the injector.
 

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I dont talk about fuelpressure with my girlfriend
 

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Discussion Starter #7
interesting - I have a Nismo fuel pressure regulator, and the top of it is plumbed into a vacuum system where my Denso pressure sensor gives readings to my PFC. So presumably, even if fuel pressure is constant in the fuel rail, fuel pressure would change in the feed and return lines based on manifold pressure (boost/vacuum)?
 

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The pressure is constant over the injectors, NOT in the fuel rail. The injector bridges the fuel rail pressure and the manifold pressure. For the difference to be kept constant the pressure in the rail has to rise and fall with the manifold pressure.
 

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Discussion Starter #9
so the feed lines to and from the rail can vary how much in pressure (low/high peaks)?
 

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The return should never have much appreciable pressure as it shouldn't be restricted from getting back to the tank.

The feed will vary by your boost pressure + maximum vacuum.

At idle you might have 450mmHg vacuum and a fuel rail / inlet line pressure of about 2.4 bar.

At 0 manifold pressure you should have about 3 bar fuel pressure. -This is the same as pulling the sensor hose of your fuel regulator.

At full boost you will have 3bar + your boost pressure, so 4 bar at 1 bar of boost.
 

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Discussion Starter #11
ah. I estimate my fuel pressure to be running high anyways (as I had to adjust my Denso 700cc injector correction to 50%, implying that the fuel pressure at idle is high enough to make them act like 888cc injectors), so add 1.4bar on top of that.

I've lost the argument (basically the argument was on fuel pressure in the lines, not the rails). Now I gotta fecking do the dishes for a week.
 

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Kismetcapitan, always agree with your gf, just say, "yes darling, you are right"
Just to keep them happy, they love being right :chuckle: lol

I, myself stopped long ago arguing with my gf :nervous:
 
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