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Old 11-28-2009, 02:32 PM   #1
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Default Epic failure to understand fueling thread

The first question I have is regarding the fpr. Car is 90, near future engine is 97, head being delivered is 00. I have the later model mtuned dual feed fuel rail. I am getting very large injectors. Because the fuel pump is probably original, or at very least old, I want a new pump, figured I would go for high flow, some Walbro or another. The question is, do I need, or should I get, some sort of adjustable fuel pressure regulator if using a high flow pump? Should it be straight 1:1 like this: M-Tuned Adjustable Fuel Pressure Regulator -6 M-Tuned or one of the Begi style fmu deals? If I get a 1:1, does the factory fpr stay? Do I have to modify it in any way if I run another afpr? Aside, why do we call an afpr 1:1 if it still has a vac port, and how does this differ functionally from the rising rate fmu like what begi sells?

More to the point, how does the factory unit work? Is it just preserving a certain pressure delta over the mani pressure reference (hence the vac line to the mani)? Is this delta set/preset in the fpr unit bolted to the factory rail, or is there another regulator? If I run any type of afpr, do I still ref mani pressure?

I did read the faq section on fueling, and did a comprehensive (not exhaustive) search here and on m.net, but still don't really understand how this works. A link somewhere would help, as well, if this has been answered elsewhere. I want to understand this.
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Old 11-28-2009, 02:41 PM   #2
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The M-tuned one will replace the factory FPR. You then have the option of increasing the base fuel pressure to give yourself more fuel capacity out of the injectors, while maintain the proper 1:1 ratio.

say you get a 190lph pump and 800cc injectors. you still dont need to replace the stock fpr unless the injectors are undersized in boost.
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Old 11-28-2009, 02:52 PM   #3
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stock fuel pump is aproximatly 160 lph so it will handle everything you have webby it just doenst flow well at high fuel pressures.
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Old 11-28-2009, 03:03 PM   #4
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Quote:
Originally Posted by magnamx-5 View Post
stock fuel pump is aproximatly 160 lph so it will handle everything you have webby it just doenst flow well at high fuel pressures.
Probably enough, just thinking that it is too old to trust.

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Originally Posted by Braineack View Post
The M-tuned one will replace the factory FPR. You then have the option of increasing the base fuel pressure to give yourself more fuel capacity out of the injectors, while maintain the proper 1:1 ratio.

say you get a 190lph pump and 800cc injectors. you still dont need to replace the stock fpr unless the injectors are undersized in boost.
I think the unintelligent should not be allowed to order these parts.

I may just stick with the factory fpr and do a new pump. What, though, is implied by 1:1? Does this just mean that, like the factory fpr, it takes a mani ref to make sure that pressure delta is always the same, even though the end of the injector sees a range of vac/pressure in the intake? This, in contrast to the fmu style which raises the effective pressure the end of the injector sees when the mani is in boost?

Does anyone think that the factory fpr will be overwhelmed by the high flow pump? Any reason whatsoever to run a afpr, other than raising base pressure to increase flow cap of the injectors? Last, is there anything to the posts by popstoy on m.net that the 99/00 head needs an injector with a delta of 60 psi, like the factory provides? If so, the afpr is a needed item.

Thanks a fuckload. I hope I can pay back some of this info in the future.
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Old 11-28-2009, 06:14 PM   #5
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ZOMG. read the FAQ.
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Old 11-28-2009, 09:49 PM   #6
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Hence epic failure. I get it now, an fmu with an 8:1 ratio will raise the base fuel pressure eight times the pressure it sees at the manifold reference. So, if you are boosting 1 psi, the fmu will raise the fuel pressure 8 psi above the base fuel pressure. The stock fpr or an afpr with a 1:1 ratio will raise fuel pressure 1 psi per 1 psi of boost referenced in the mani. Without any rising rate control, the actual fuel pressure provided at the end of the injector in the pressurized manifold tract will decrease with an increase in boost, leaning out the mixture in boost.

Also from the FAQ: "The 255 flows more fuel at any giving pressure level than is needed. They tend to overload the OEM FPR and cause the system to run rich even in vacuum."

There I am.
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