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?

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.

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.

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

installing an FMU in your 99 isnt that hard.

Just pondering other options. :) I currently use a walbro 190HP.

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

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.

Complex systems are complex. But all else being equal, Ohm's Law comes into play eventually.


Really?

Dual fuel pump that bitch and do a small loop for the returnless.

dumb as fuck.
also: my walbro 255hp did not overwhelm the stock fpr, so your stocker (or 190) wont, despite you raping it in the ass with voltage

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.

Look up Fuelab fuel pumps. You can send them a 1k Hz PWM control signal to decrease/increase fuel flow as needed. Slick setup.

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.:dunno:

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.

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.

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.

:giggle:

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.

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.

see post #5

See post #21.

You forgot to post the link.

It was a nerd joke. By telling Scott to see post #21 from within post #21, I created a recursive loop.

you're such a fascist

You got it wrong, check this out.

https://www.miataturbo.net/showpost.php?p=803588

:bowrofl:

Very clever. I wasn't even thinking in that direction.

I didn't mean to start an arguement with this thread, I just like to think of different ways to accomplish the same goal. My thought process was basically this-

Creating a full return system requires either modifying the existing rail or installing a different one, an afpr, and all the necessary plastic fuel line.

A dual pump setup requires you to plumb the FMU between the existing pump and fuel rail. Then loop the FMU around the inline, so the inlet of the FMU branches off from the fuel line after the inline pump and the return of the FMU branches off just before the inline. (stole from :brain:)

A boost-a-pump requires the unit and tapping into one wire at the pump.

Now, the first two methods are well tested and work great, but maybe the third method will work as well, and seems to be much cheaper and easier to install. (600hp blown mustangs and vettes use them.)

I have the powertrain out of the mazda at the moment so any of the above would be cake. Still thinking it over.....

Honestly, I've already been accused of being closed-minded twice today, and I have no empirical evidence that over-volting the stock fuel pump in lieu of installing a more traditional form of engine management will result in either the failure of the fuel pump or the destruction of the engine due to an overly lean mixture in boost.

So I retract everything I've posted in this thread.

Wanna hug it out bro? :makeout:

I thought the "Bro" talk was banned.

A well known tuner/shop recently installed the kb boost-a-pump onto his built big power sti and did testing.

the pump (a wally 255 iirc) died after a few weeks and he leaned out like crazy....don't remember if he broke anything in the process.

the point is, some things are just not worth trying to work around. like good engine management....*hint hint*

Why couldn't you do something like FM's big fuel kit and remove the stock in tank FPR and place a AFPR near the tank with only one big line to the engine bay. It's not a "proper" return system but you could adjust the fuel pressure to whatever you want. I suppose you could even skip upgrading the line to the engine bay to keep things simple.

See here: http://flyinmiata.com/index.php?dept...umber=04-46150

And a picture here: http://flyinmiata.com/Store/images/04-46150a.jpg

EDIT: Looking at this post (http://forum.miata.net/vb/showpost.p...0&postcount=16) and reading FM's description again, the APFR would be located near the stock fuel filter.