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Old 12-03-2011, 03:08 PM   #1
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Default Increasing FP voltage vs. AFPR

Since I own a 99 with a returnless fuel system, installing an afpr isn't the easiest thing to do. What if you use increased voltage to increase the output of the fuel pump instead? It should be able to blow past the in tank regulator and provide more pressure to the rail when you need it.

Seem plausable?
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Old 12-03-2011, 04:08 PM   #2
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Fuel pressure at the rail is a function of the fuel pressure regulator.

Now, we know from experience that it's possible to force enough fuel into the system to exceed the bypass capacity of the FPR (eg: with a Walbro 255) however this isn't a very pricise way to handle fueling. And to achieve this by over-volting a stock fuel pump? Seems like you'd destroy the pump before you increased its output sufficiently to overwhelm the stock FPR.

This is a bad idea.
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Old 12-03-2011, 04:09 PM   #3
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Edit - ^Beat me to it......

Correct me if I am wrong but I don't think more voltage to an electrical component INSIDE of a gas tank is the smartest of ideas. That being said, you would burn out the motor really fast for the amount of voltage you need to up the pressure if it even works like that. Just drill/tap the other end of the fuel rail like everyone else.
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Old 12-03-2011, 04:26 PM   #4
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A fuel pump is just an electric motor. The more voltage you send to it (within reason) the faster it will spin.

I did some googling and found that Kenny Bell beat me to it.

Great read! http://kennebell.net/techinfo/genera...heory_kens.pdf
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Old 12-03-2011, 04:28 PM   #5
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installing an FMU in your 99 isnt that hard.
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Old 12-03-2011, 04:42 PM   #6
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Just pondering other options. I currently use a walbro 190HP.

http://kennebell.net/techinfo/genera...heory_kens.pdf Here is another discription.

Last edited by flounder; 12-03-2011 at 04:59 PM.
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Old 12-03-2011, 09:51 PM   #7
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Quote:
Originally Posted by Joe Perez View Post
Fuel pressure at the rail is a function of the fuel pressure regulator.

Now, we know from experience that it's possible to force enough fuel into the system to exceed the bypass capacity of the FPR (eg: with a Walbro 255) however this isn't a very pricise way to handle fueling. And to achieve this by over-volting a stock fuel pump? Seems like you'd destroy the pump before you increased its output sufficiently to overwhelm the stock FPR.

This is a bad idea.

IDK, you could argue that using a restriction in the line to increase pressure puts more strain on the pump, than increasing voltage would. You could control it with a hobbs switch to increase voltage only under boost and get the benefit of smaller injectors which would help idle conditions.

With just my 190hp I see 62psi at idle. With the old one it never built up over 58psi, fpr is set for 60psi. I bet one or two more volts would bump that up to 70.
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Old 12-03-2011, 10:08 PM   #8
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Quote:
Originally Posted by flounder View Post
IDK, you could argue that using a restriction in the line to increase pressure puts more strain on the pump, than increasing voltage would.
Complex systems are complex. But all else being equal, Ohm's Law comes into play eventually.


Quote:
You could control it with a hobbs switch to increase voltage only under boost and get the benefit of smaller injectors which would help idle conditions.
Really?
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Old 12-04-2011, 01:08 AM   #9
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Dual fuel pump that bitch and do a small loop for the returnless.
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Old 12-04-2011, 01:30 AM   #10
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dumb as ****.
also: my walbro 255hp did not overwhelm the stock fpr, so your stocker (or 190) wont, despite you raping it in the *** with voltage
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Old 12-04-2011, 01:45 AM   #11
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It might overwhelm the fpr at idle or when you rev it up, but I bet if you made a pass while watching the pressure, you'd watch go right back to regulated pressure when you need it most.
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Old 12-04-2011, 11:42 AM   #12
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Look up Fuelab fuel pumps. You can send them a 1k Hz PWM control signal to decrease/increase fuel flow as needed. Slick setup.
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Old 12-04-2011, 01:56 PM   #13
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Nice! I was reading about the boost-a-pump and it's a single wire installation vs. running a return line or using an aux pump, larger injectors, etc.

Since I still use an emb, I need to watch my injector size. If I can pick up a used unit for like a $100, I may try it out.
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Old 12-04-2011, 02:09 PM   #14
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I still can't imagine why you'd want to try something as hairy and unpredictable as this, rather than installing an inline pump and AFPR under the hood.
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Old 12-04-2011, 02:37 PM   #15
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Multistage fuel pumps actually are not uncommon in many stock OEM applications as well as mid to high end aftermarket applications--especially when running fuels other than gasoline.
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Old 12-04-2011, 03:06 PM   #16
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Yeah, I know. And the current-gen Subarus use PWM to adjust the power to the fuel pump in response to demand.

Doesn't change the fact that trying to manage the fuel supply of an NB by over-volting the stock pump is going to be unpredictable at best and cause failures at the worst. I can see no reason not to install an inline pump under the hood and create a local recirculating loop through a rising-rate FPR. That's the easiest way to achieve stable, controllable fueling given the requirement not to embiggen the injectors.
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Old 12-04-2011, 03:24 PM   #17
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Quote:
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given the requirement not to embiggen the injectors.
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Old 12-07-2011, 12:15 AM   #18
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I've been looking into a few options for running a walbro 255 in my NA lately... Currently leaning toward using an acura RL fuel pump resistor with a relay to create a two speed setup, i.e. at some level of boost take the resistor out of the circuit. Surely with a bit lower voltage the stock NA FPR can deal w/ a 255. The sexier option is to get a Ford FPDM which is basically an amplifier/PWM multiplier and drive it with my MS3 via one of the generic PWM outputs, there's a guy whose at least proved its possible on locostusa.

An even sexier option is to run this guys board: http://www.madhu.com/content/Main/FuelPumpController and go returnless... But alas, the ford and gm ppl have figured out that the gerotor walbro's die an early death because the circuits end up sending them too low of a voltage. The DW and new aeromotive stealth pumps don't have this issue tho as they're turbine pumps... I'm just not sold enough on the idea to take it to that level though... Someone else should be the guinea pig.
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Old 12-07-2011, 05:45 PM   #19
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This whole thread is predicated on blind acceptance of the false notion that implementing an AFPR on an NB is hard.

And that makes me sad.
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Old 12-07-2011, 05:48 PM   #20
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see post #5
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