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Old 05-15-2002, 11:05 PM   #1
bobgrice
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2002 WRX Sedan
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Default Fuel Pressure Question (can't search)

Sorry if this has been covered, but as you know we can't search for a while.

My plans are to wring as much as possible out of the stock turbo and fuel setup before upgrading to larger units - just to see what it can do.

I have a fairly lengthy mod list, but it doesn't include any fuel mods (stock pump, injectors, rails). My list can be condensed into a full complement exhaust mods, significant intake mods (including ported turbo), and custom-mapped Unichip - along with many other bolt-on's.

I have a fuel pressure gauge which I will be installing this weekend alond with some other double secret goodies.

I have good information on what pressures to expect under what conditions, but my question centers around others' experience on a reasonably modified vehicle while using the stock turbo and fuel system.

Has anyone with significant mods, but still running the stock turbo and fuel system, experienced fuel pressure problems from the stock pump? I am looking for experience from folks with a fuel pressure gauge or datalogging that could tell them if they have seen any limitations.

Also, would I expect to overtax the stock injectors before the stock fuel pump or vice-versa?

Thanks for any guidance.
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Last edited by bobgrice; 05-16-2002 at 09:36 AM.
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Old 05-16-2002, 09:37 AM   #2
bobgrice
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Default

Bump

Please...

help...

me...
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Old 05-16-2002, 11:26 AM   #3
Jon [in CT]
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Default Re: Fuel Pressure Question (can't search)

Quote:
Originally posted by bobgrice
I have good information on what pressures to expect under what conditions, but my question centers around others' experience on a reasonably modified vehicle while using the stock turbo and fuel system.

Has anyone with significant mods, but still running the stock turbo and fuel system, experienced fuel pressure problems from the stock pump? I am looking for experience from folks with a fuel pressure gauge or datalogging that could tell them if they have seen any limitations.

Also, would I expect to overtax the stock injectors before the stock fuel pump or vice-versa?
My understanding of how the stock WRX fuel pressure regulator works is that it's designed to maintain a fuel line pressure of 43 PSI, +/- whatever the relative manifold air pressure is. If this is true, then if you were able to make your fuel pressure gauge read zero when the actual fuel pressure is 43 PSI, then it would move more or less in tandem with your boost gauge. If at high RPMs and load you were to notice this relationship to "break down" (i.e. fuel pressure starts to read less than it should, relative to boost), then you might conclude that your fuel pump has maxed out.
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Old 05-16-2002, 12:00 PM   #4
Z1 Performance
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Default

Jon - exactly - that's how it works on turbo cars. The stock regulator is 1:1, meaning it adds 1 lbs of fuel for every 1 lb of postitive manifold pressure it sees (postive manifold pressure=boost). Stock pressure at idle is betwwen 39-43 according to the specs (I haven't come accorss a car with under 43 yet, nor any over for that matter). So, at 15 psi of boost, fuel pressure should be around 58 psi.

As Jon said, if you find that at high rpms your fuel pressure trails off, then its time to upgrade the pump. Once the pump is upgraded, if at idle you then find fuel pressure to be higher than 43 psi, it's time to upgrade the regulator.

Given the level of stuff you ahve planned, I think you'll be perfectly fine with the stock stuff as long as you keep to moderate bosot levels, and use the highest octane gas you can buy near you....I would also make a decent datalogger and EGT part of the mod list, just so you can routinely keep tabs on things

adam
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Old 05-17-2002, 05:47 PM   #5
bobgrice
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Default

Thanks, Jon & Adam.

I will take this to heart.

With my OBDII datalogger and EGT gauge, A/F gauge and Fuel Pressure gauge with warning lights, I should be in good shape.
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