Fuel pressure with Walbro pump?
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This is a discussion on Fuel pressure with Walbro pump? within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; Anyone with a fuel pressure gauge and a Walbro fuel pump out there? I'm just wondering how much the pressure ...

  1. #1
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    Fuel pressure with Walbro pump?

    Anyone with a fuel pressure gauge and a Walbro fuel pump out there? I'm just wondering how much the pressure increases with the new pump.

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  3. #2
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    the fuel pressure is limited by the fuel pressure regulator(FPR)...the pump is capable of much more than we need.

    the Factory FPR is setup on a 1:1 ratio...for every 1 PSI of boost it raises the fuel pressure 1 PSI over static pressure which (IIRC) is ~40PSI....so if your running 15psi of boost the you should be running 55psi.....

    the reason for the ungrade is not only flow but the higher pressure allows for proper fuel pressure where the stock Fuel Pump cannot sustain +60psi easily...
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    Quote Originally Posted by testes1010
    the fuel pressure is limited by the fuel pressure regulator(FPR)...the pump is capable of much more than we need.

    the Factory FPR is setup on a 1:1 ratio...for every 1 PSI of boost it raises the fuel pressure 1 PSI over static pressure which (IIRC) is ~40PSI....so if your running 15psi of boost the you should be running 55psi.....

    the reason for the ungrade is not only flow but the higher pressure allows for proper fuel pressure where the stock Fuel Pump cannot sustain +60psi easily...
    I understand the need - but every FPR I've seen is an orifice type in the fuel return line with the size of the orifice calibrated to the flow of the stock fuel pump. You put a pump in place that flows a lot more through the same size orifice you end up with higher rail pressures.

    I put a Walbro in my RX7 with an adjustable rising-rate fpr. The fpr was set to give stock fuel pressure (38psi static) with the stock pump. When I switched to the Walbro the pressure jumped to 55 psi.

    If you're going to tell me that fpr has a feedback loop that lets it actually read what the pressure is and then adjusts it that's one thing; otherwise I can't see how the rail pressure can't increase. Do you have a fuel pressure gauge?

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    I have a fule pressure guage, but my walbro pump sits in my garage. I think the pressure will rise so I have therefore not installed it, and don't plan on doing it before I change the ecu.

    I'm not sure, but I cannot understand how the stock FPR could retain stock pressure if you rise the input pressure. It's impossible by design...
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    No one has a walbro and a gauge out there?

  7. #6
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    pm REX NFX on WRXFanactics.com, he has one...
    1988 Celica Alltrac
    Hallman Pro, 15x7.5 +20mm Rota Slipstreams
    2005 LGT 315whp/340wtq@21psi - Sold
    VF52, Crucial P&P&C Manifolds, UP, DP, RP, Magnaflow CBE, Hallman PRO, ROMRaider
    2003 WRX 371whp/355wtq@24psi - Sold
    TD05H-20G-38mm Tial, Meth Injection, Hyperflow TMIC, ROMRaider
    Dyno Chart METH vs 93 oct

  8. #7
    Wrinklechops
    Quote Originally Posted by tshrey View Post
    No one has a walbro and a gauge out there?
    I'm bringing this one back from 6 feet below... but I am planning on logging some data regarding fuel pump pressure, etc tomorrow before I put the Walbro in and then log afterwards and see what we come up with

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    The post was for my 02 WRX - and I eventually got my answer by putting in an underhood gauge. On a WRX the static pressure went from 38 psi to 42 psi. On an STi I would imagine the difference would be much smaller, possibly none. It looks like the flow potential in the WRX fuel system was much higher than in my RX7 so the orifice must be considerably larger.

    From what I've read my 08 STI has a larger stock fuel pump, so the jump up to a Walbro is smaller, possibly not changing the static pressure at all.

  10. #9
    Wrinklechops
    So basically, the less static pressure the better? Or the more the better?

    I am going to log with Romraider like Fuel Pressure and Fuel Pump info with and without the Walbro just for fun. Not sure what sort of numbers I should expect to see, but at least I'll have the data saved in case I ever run across an answer and then I can remind myself the Walbro was worth the $$$

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    Unless you are going to protune the car, you ideally want the same pressure so that nothing has changed. If it does go up you can change the effective size of the injectors in the tune to keep things the same.

    The limitation of the stock pump is that as boost pressure increases the fuel pressure is increased and the flow rate will drop. The Walbro has lots of overhead so its output won't drop as pressure rises.

  12. #11
    Moderator Donkey's Avatar
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    Quote Originally Posted by lundholm08 View Post
    So basically, the less static pressure the better? Or the more the better?

    I am going to log with Romraider like Fuel Pressure and Fuel Pump info with and without the Walbro just for fun. Not sure what sort of numbers I should expect to see, but at least I'll have the data saved in case I ever run across an answer and then I can remind myself the Walbro was worth the $$$
    Unless you are tuned for it you don't want static pressure to change at all.If fuel pressure goes up you have to rescale your injectors because more fuel is squeezing out per IPW.Also you cannot log fuel pressure in Romraider.Just fuel temp,tank pressure and fuel pump duty cycle.
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  13. #12
    Wrinklechops
    Quote Originally Posted by Donkey View Post
    Unless you are tuned for it you don't want static pressure to change at all.If fuel pressure goes up you have to rescale your injectors because more fuel is squeezing out per IPW.Also you cannot log fuel pressure in Romraider.Just fuel temp,tank pressure and fuel pump duty cycle.
    Great so it may be a bad thing to put the Walbro in if I'm not tuned for it? I was talking to my friend who was talking to our local tuner if you will and he said it's not really necessary until I get a VF39 but it's a good idea to have and doesn't require tuning....

  14. #13
    Wrinklechops
    What is the fuel pressure at idle typically for example? Mine is stuck at 33 with the Walbro pump and an old dirty fuel filter probably. I wanted to check real quick before I go out to the garage and change my fuel filter as it just arrived in the mail. If the Walbro is junk, it'd be a nice time to know before I start to wreak of fuel lol

  15. #14
    Moderator Donkey's Avatar
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    Quote Originally Posted by lundholm08 View Post
    What is the fuel pressure at idle typically for example? Mine is stuck at 33 with the Walbro pump and an old dirty fuel filter probably. I wanted to check real quick before I go out to the garage and change my fuel filter as it just arrived in the mail. If the Walbro is junk, it'd be a nice time to know before I start to wreak of fuel lol
    At sealevel with the vacuum line removed(and plugged) from the FPR it should be 43.5 psi.
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