So things are something like that ?:

NA fp is 3bar none boost and boost - vacuum referenced.
NB (01-05) (fpr in tank) 4 bar none boost and "4-boost" in boost - not vacuum referenced.

Correct ?

Yes. But remember its not just "vacuum" referenced. Its also boost referenced. So as manifold pressure increases so does fuel pressure.

So vacuum/boost referenced will keep to fp constant - right ? 3 bar vacuum or boost - at boost the fp is "fp-boost = 3 bar".

It keeps pressure at manifold constant by raising/lowering rail pressure.

probably a stupid question, but I would like to increase fuel pressure on my project miata ( in process of building) which will be runing ITBs with big cams. I want to increase fuel pressure up to 4Bars, and want to run injectors at about 60-65% Duty cycle. That mean I am looking at injector of about 340cc min@3Bar, which should give me about required 390cc/min at 4Bars.
My question is although following:
- Can I run fuel pressure regulator that is intended to be used with vacuum reference without vacuum reference ? I am looking for this regulator at the moment, as I think that is ideal for what I need.
https://www.carid.com/fuelab/fuelab-...748441522.html
Question is, how will the regulator like this that is intended to be used with vacuum reference work without it ? will it stay at my pre set value ? I believe so, as it is 1:1 and hence at atmospheric pressure which is pressure what it will see when no vacuum will be connected it should be stable as the pressure does not change right ? Am I missing something that would force me to use vacuum reference on this regulator ?
Thanks and sorry for my lack of knowledge in this topic in general. I hope someone well educated can chime in.

I'm a simple beginner, to dangerous for my own good, but here goes from my understanding and what Aeromotive has noted in their FAQs, regarding their bypass regulators. I assume the NA regulator operates the same way?

The atmospheric reference pressure is your baseline. Vacuum will reduce the amount of pressure and pressure will increase at a 1:1 ratio. Where it can get quickly confusing and needs to be kept straight are the different units of measure commonly used for pressure and vacuum.

From
FAQ ? EFI Regulators ? Aeromotive, Inc
All Aeromotive, EFI bypass regulators incorporate the necessary design to allow the regulated fuel pressure to be vacuum/boost referenced on a 1:1 ratio with PSI. Always connect a vacuum/boost line between the intake manifold and the regulator cap for port fuel injected engines, forced induction or natural aspirated, where the fuel injector discharges into the intake manifold after the throttle body. Remember to set base fuel pressure with the vacuum/boost line disconnected from the regulator. For TBI engines or applications where the injector discharges above or before the throttle blade(s), the vacuum/boost port should be left disconnected and open to atmosphere, never blocked or plugged. Note: the ratio of 1:1 is measured in PSI. When looking at a vacuum gauge, it is normally calibrated in “HG or inches of mercury. It takes roughly 2”HG to equal 1 PSI. So, for example, when the vacuum gauge reads 10”HG, with the engine at idle, fuel pressure will drop 1/2 of that or 5 PSI.

I'm installing one of these in the near future.

Connect it to vacuum off of the back of intake manifold.

I was not asking where to connect vacuum line. I was asking if it is possible and ok to run this AFPR without vacuum reference. Running vacuum line on big cammed car with ITBs is nonsense.

You can run it without the vacuum line connected (put a cap on it) which will result in non-variable fuel pressure.

are you sure about that? The guy on top of you quoted: "For TBI engines or applications where the injector discharges above or before the throttle blade(s), the vacuum/boost port should be left disconnected and open to atmosphere, never blocked or plugged" .

Hm... That kind of makes sense since the diaphragm is going to be pushing air in/out of that hole when it flexes. I would need to take one of the units apart to tell you for sure.

Andrew, you may not be fully understanding the quote from Aeromotive's website?
.
Specifically about the quote, it is in regard to Throttle body injection (TBI), not port injection. From my understanding, no Miata has ever had a TBI fuel injection system. It's a first gen sort of approach to fuel injection, precursor to port injection. So, it really doesn't apply (unless I'm seriously missing something here). The reason for Aeromotive's concern is that you don't want upstream fuel in air getting into the regulator body via its sense line. Yet, the sense line to the regulator, at a minimum, should be open to atmosphere. If you leave it open to atmosphere, it should have some sort of little filter on it to keep it from contaminants into the reg body. I suppose it would be a non-issue (plugging it) if you never intend to change the car's relative altitude- yet, folks like Aeromotive have to CTA.

If you want to hold the pressure constant, why not just convert to a "return-less" system?

I can't even.........................comprehend how stupid this got

Never plug them. There is a spring which sets the base pressure. If u connect it to your manerfod you offset the spring pressure with your intake pressure. So that your fuel pressure relative to your intake is constant. But when you plug it you change your spring rate from linear to raising backpressure.

So the advice is to leave the FPR vacuum not connected and not plugged ... confirm please

No the advice is to run a vacuum line. but if somebody is to ignorant to do so then at least dont plug. If you dont run vacuum you change your fuel pressure dependent on engine load all the time.

Better yet, install carburators :D

So my engine builder told me to set the FPR at 48 PSI and then tune from there. I have non FI build. I asked him why should the FPR not be connected and he said to leave it unconnected to the vacuum. I also was sort of confused and wondered when this post showed up whether I got bad advice. I have a square top with Skunk TB. I need a vacuum for MS and now I need one for FPR. Should I put a T to feed both. I have not yet figured out where to get the best vacuum from Square top for MS or FPR.

He told you to leave a fpr disconnected? And you let him build your engine?

I did and handed him a fat check. He is a well known SM engine builder. Maybe it's my hearing and I had a senior moment and did not get it.
I wasn't even sure why FPR for NA build and Megasquirt with stock injectors.