Fuelab 545 used as returnless?
 

Is it possible to run the Fuelab 545 external to the fuel tank but still work similar to the returnless system?

I may have to replace my fuel pressure regulator and I would prefer to keep it as simple as possible.

The 545 is meant to be an inline return style regulator, that would be placed after the fuel rail. If you are wanting a returnless regulator, you would want the 555 series.

Contact Advanced Autosports for a 555 that was designed for the Miata pressure range. The part number is 55504.

Thanks!

Could you move it out of the tank and put it under the car where the filter lives? I'm not sure if that is a "safe" or "correct" location, but the lines are all there, and its convenient.

Check this thread for what I'm talking about: https://www.miataturbo.net/diy-turbo...l-style-74629/

I don't see why you couldn't use the 545 with no vacuum reference? I may be ritarded though.

The 545 just cannot be used as a returnless/blocking regulator. It simply won't work. The 555 is the only returnless regulator that Fuelab offers.

Ideally, the regulator would be in the engine compartment. The closer it is to the rail, the better (blocking or return style). This is especially true in a boosted application when the boost reference port is being used in order to raise the fuel pressure 1:1 with boost.

That's obviously ideal, but OP here has NB, NB has no return and the "blocking" regulator is located inside the tank. Linked thread shows converting an NB to return, also shows where the fuel lines and the T for the fake return to the in tank regulator is located on the NB. Pretty sure you don't want to install either 5x5 INSIDE the fuel tank.

What I'm saying is read the linked thread, install 545 at the T with no vac reference, remove in-tank blocking regulator, plumb return back into the tank, set pressure, win at life. I don't have time to bust out the MSPaint right now.

I don't see why it WOULDN'T work, and yes I know its not ideal, either in design or location but the NB returnless system is less than ideal anyway. Hopefully someone smarter than me can comment, I'm just spitballing here.

I misunderstood- I thought you were wanting to use the 545 as a blocking regulator. That regulator won't.....well, block.

I'm not familiar with the Miata, I just know aftermarket fuel systems. Advanced Autosports likes to leave the factory regulator as-is and use the 55504 downstream mounted in the engine compartment to knock the pressure down to 50psi.

No worries, that's why I jumped in to clarify :bigtu:

Also, I see you have 3 posts and all of them are in this thread. Time to go make an intro thread and denoob thyself: Meet and Greet - Miata Turbo Forum - Turbo Kitten is watching you test compression.

I can get a 555-series regulator if you want it - most guys who do a regulator swap to a return-style system at the same time, so most of my experience is with the inline-style 545.

What is the benefit of a return style vs returnless?

In short, return style system is easier to tune and the system can react to changes more or less instantly. In most factory equipped cars, there is some sort of fuel pressure sensor or something controlling the output of the pump- the output nearly matches the need of the engine. When there are changes (such as boost coming on), that makes it harder to tune because it takes more time for the fuel system to react. With a return style system the flow is always there when needed.

That's not to say returnless cannot be tuned correctly for high horsepower applications, because there are many tuners that are good at it. The main problem is that a lot of aftermarket pumps cannot be ran deadheaded/returnless and the factory pump controllers are not compatible with the aftermarket pump.

I can't say I'm aware of any car that uses an electronic fuel pressure sensor and variable speed fuel pump to regulate fuel pressure or volume. I'm not saying they don't exist, I've just never seen one. A traditional regulator is far easier and cheaper for an OEM to manufacture and deploy rather than a fancy electronically regulated system. I don't see any significant benefit of a return over a returnless system on an NA car. Once you add boost, I can see serious benefits on a MAP referenced return system.

A non referenced system will lose pressure and volume in a 1:1 relationship to manifold pressure. The (example) 43.5psi fuel pressure at the rail has to fight the 12psi you are pushing into the manifold with no way to compensate, so now you only have 31.5psi at the injector and your 650cc injectors are now only 553cc. This drops your volume delivered and forks up your spray pattern. (Think about pulling the trigger on a spray bottle slowly as opposed to furiously pumping away at it.) Now you need even larger injectors and longer injector pulses just to get your AFRs to a safe level at that 31.5psi. Generally speaking, larger injectors will have crappier spray patterns* to start with, so now you are running a larger injector and less pressure. Granted it is linear and can be tuned around, but its not ideal in any sense and requires compromises.

With a manifold referenced return regulator, your 43.5pis (example) fuel pressure can rise 1:1 in relation to boost so you can expect consistent fueling in volume and spray pattern. Your 650cc injectors are always 650cc because you always have an effective 43.5psi in the rail and your spray patterns are going to be consistent. It should in theory make tuning easier and more predictable.

* Newer technology injectors such as the EV14 can mitigate a lot of this. We have guys running 1000cc EV14's and idling stoich with no issues. Good luck trying that on 1000cc EV1 tech :giggle:

I can't speak for the Miata but nearly all other factory returnless cars have some sort of a FPDM/Fuel Pump Driver Module that varies the voltage to the pump which is how the pressure is controlled. The FPDM decides what to do based on what the fuel pressure sensor on/near the rail tells it. A pump (factory or not) cannot be deadheaded all the time while still running at full speed. Most OEM's will vary voltage to slow the pump down on a deadhead/returnless system. Some of the exotics use a PWM to control the speed of the pump rather than a voltage change.

Outside of that, everything you said is correct. Return style easier to tune and can react quicker to changes in fuel pressure due to the system being mechanical (the pump is already running at full speed, only the spring/diaphragm in the regulator has to react to a change). Additionally, if the regulator is up close to the real, it's monitoring the fuel pressure where it really counts (at/near the injectors) rather than back by the tank.

See, this kind of information is what makes this forum rock. Once I go return style, does it cause any headaches for the stock computer for when it has to drive me to get emissions tested and back?

Glad I could help! :party: I'm not the smartest hammer in the drawer, but I try to maintain a solid signal:noise ratio (unless I've been drinking then all best are off)

If you are on stock injectors and stock computer, you will need to run the stock NB 60psi rail pressure to keep things from freaking out. The ECU can compensate within reason, but its "tables" are only so big. Set the FPR to 60psi, remove the vacuum reference, pass smog like a bauce.

The Miata has none of the electronic fuel pressure volume control wizardry that bumpnzx3 is describing above, its just a dumb regulator. NA have vacuum reference with return at 43.5pis and NB have non-return fixed regulator at 60psi. (Except it's kinda a return... regulator is in the tank, see that thread I linked earlier)

I'm basically doing exactly what you asked and I just described, except CA so I need it to look OEM :bang:

Do you have a visual inspection that goes along with your SMOG? I know some states do (such as CA mentioned above), in which case you might have problems. I'm in Illinois (just OBDII), but next door in Missouri there's a visual as well.

It's not "control wizardy"- it's quite common. My beater Focus has it, Mustangs have it, LS1 cars have it....pretty much all modern Ford and GM cars have it (what I'm most familiar with).

*Edit*
Just did a quick Google search- many modern Mazdas use said wizardy as well.....but apparently not the Miata.

CA has visual, its all kinds of sadness :(
...but we drive Miatas around here. I mean, its good data for the sake of data (I know I learned something) but its outside the scope of the current conversation.

We (Illinois) do not have a visual, but the folks next door in Missouri do. There are many different independent shops that do the inspections (I assume the same for you). It's not all that uncommon around here (I live near the border of the two states), for there to be a bit of a "shady" shop that the performance cars end up getting their inspections done. Hahahaha!

I know exactly what you mean. Here in CA it was fairly common to know a guy who knows a guy who knows a guy that was willing to be a bit liberal on the visual inspection as long as the car would blow clean on the actual sniffer test. Its getting harder and harder to be an automotive enthusiast on the left coast. :cry:

There is no "visual" inspection in MO. OBD2 in select counties and a statewide safety inspection for things like brake pads, tires, uncracked windshields, etc.