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Old 08-15-2015, 06:33 PM   #41
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With a stock volume fuel pump you could *probably* use the 1/4" return without issue. As an exercise, unplug the return with the car running and see for yourself how much fuel is returned. I do this to take two gallons out when I go nutty at autox's and think the weight is going to actually make me quicker. It takes like 15 minutes to get two gallons out.

If I had an option of running a vacuum FPR or non-vacuum, I'd go with non-vacuum. Why have a mechanical part do what an electronic part can do better? I understand you would want it for boost reference to raise fuel pressure but you are also putting a lot of faith in the regulator and vacuum hose. Not saying its going to go bad but why take the chance when properly sized injectors and a tuneable ECU makes it less work and more reliable.
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Old 08-15-2015, 07:29 PM   #42
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Originally Posted by DNMakinson View Post
<p></p><p>But, the CL idle takes care of the extra load by adding air. Fuel formula (MAP goes&nbsp;up)&nbsp;and VE table then handle the fuel for us.
And then idle speed goes up as vacuum does, if closed-loop idle were to work that way (it doesn't). In reality, the car richens and leans itself out in a feedback loop based on fuel pressure, which means it will never idle like it should. You cannot cope for wandering fuel pressure at idle with closed-loop idle algorithms effectively.
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Old 08-16-2015, 12:23 AM   #43
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If I had an option of running a vacuum FPR or non-vacuum, I'd go with non-vacuum. Why have a mechanical part do what an electronic part can do better?
One advantage to using a referenced FPR is that with lower fuel pressure at idle you won't suffer as much from using big-*** injectors.

--Ian
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Old 08-16-2015, 12:58 AM   #44
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Why is the nb system return less anyways?
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Old 08-16-2015, 01:06 AM   #45
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Why is the nb system return less anyways?
IIRC, it's because cycling the fuel through the engine bay like that heats it up, which increases evaporative emissions. Pretty much all cars since 2000 or so are non-return systems.

--Ian
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Old 08-16-2015, 08:34 AM   #46
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One advantage to using a referenced FPR is that with lower fuel pressure at idle you won't suffer as much from using big-*** injectors.

--Ian
Yes and as stated before so you can use a rising rate FPR which again means you can use a smaller injector to achieve the HP goal. Which means you will have an even smaller injector to control at idle.

The difference is about 10lbs of fuel pressure at idle on an engine that has healthy vacuum of 40kpa (60kpa) (invert of 60kpa). So lets say 1000cc injectors at 45psi flow 1000cc and at 35psi they flow 880cc.

So its about a 10% difference. Admittedly that's a difference...... but you still have a 900cc injector at minimum. Its still a big *** injector that you have to control at idle. It may no longer be Nicki Minaj big but its Jessica Biel big. Either way you are in for a ride.

However, if you know you are going to be using 60psi as a base with a vacuum FPR and you need 1000cc you start with 850cc which gives you 1000cc at 60psi. Well at 50psi you still get 900cc.

So the only way you make the argument that the vacuum FPR will help idle by having lower injector flow to control is if you use a rising rate FPR that can get to say 90psi. Then you can use a 750cc injector to get to 1000cc at 90psi. And that injector will flow about 670cc at 35psi.

So a 670cc injector will be easier to tune at idle and maybe is not considered big *** anymore. Maybe now its only Jennifer Garner big. But this brings me back to the point about using mechanical parts to do the job electronic parts can do. I have read several times on this forum of success stories using 1000cc ID injectors and good idle fuel control. Of course that was with a good ECU. Quality components go a long way. And I've been reading on this site about a new generation of injectors that are even better. So why go to the trouble of relying on a mechanical part to make sure that you have enough fuel when you need it?

You can tell i have nothing better to do on a Sunday morning as I drink my coffee.

Last edited by hector; 08-16-2015 at 10:32 AM.
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Old 08-16-2015, 10:02 AM   #47
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<p>Hector, in my case, the difference at idle of the vac referenced, though small, is just enough to get me out of the ugly non-linearity area of my injectors. The other reason to go referenced is to minimize severity and length of time of hot restart lean due to hot injectors.&nbsp;</p>
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Old 08-16-2015, 10:24 AM   #48
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David, no argument that it helps a lot of people maintain good idle AFR's. But just a quick glance of your build thread tells me you don't have "big ***" injectors. Nice build BTW.

On the second point, I would have to disagree with you. I don't see how having less fuel pressure can help lean hot restarts. Wouldn't mind an explanation on this.

I think you mean the reason to go return fuel, not referenced FPR. Going return fuel would definitely help in this matter. In any case, adding fuel or extending fuel in the after start enrichment table should take care of this.
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Old 08-16-2015, 10:39 AM   #49
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Why is the nb system return less anyways?
Maybe because when you are an engineer and assigned to the fuel system, you need to do "something" to make your mark.

Too bad this one missed the mark.
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Old 08-16-2015, 10:59 AM   #50
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<p>
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Originally Posted by olderguy View Post
Maybe because when you are an engineer and assigned to the fuel system, you need to do &quot;something&quot; to make your mark. Too bad this one missed the mark.<img alt="" src="http://www.miataturbo.net/images/smilies/vash.gif" title="vash" />
</p><p>Codrus in post #45&nbsp;is correct. Patents around the dampers reveal this.&nbsp;</p>
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Old 08-16-2015, 12:01 PM   #51
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Originally Posted by hector View Post
But this brings me back to the point about using mechanical parts to do the job electronic parts can do. I have read several times on this forum of success stories using 1000cc ID injectors and good idle fuel control.
I run id1000s with the MS3, and while the idle fuel was acceptable when using a fixed base pressure, it is better now that it is manifold-referenced.

It's not a case of "relying of mechanical parts to do the job of electronics". The mechanical parts build a foundation and the software builds on that foundation. The better the foundation the better the end result.

--Ian
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Old 08-16-2015, 01:04 PM   #52
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Quote:
Originally Posted by codrus View Post
IIRC, it's because cycling the fuel through the engine bay like that heats it up, which increases evaporative emissions. Pretty much all cars since 2000 or so are non-return systems.

--Ian
I can understand that the fuel will pick up heat circulating through the engine bay.

But I wonder what the difference is between this heat and the amount of heat generated by pumping the fuel over a relief valve at 60 psi continuously. The heat is generated at both the pump and the valve, to say nothing about the longevity of the pump.....
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Old 08-16-2015, 01:13 PM   #53
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There is a return system, its just in the tank. The fuel pump is not dead-heading, its going to the FPR which is in the tank and the FPR is returning the fuel to the tank without it going to the engine. Its not vacuum referenced for obvious reasons but I guess you could make it vacuum referenced if you really wanted to.

Edit: and the pump is not really building any more heat
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Old 08-16-2015, 02:03 PM   #54
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But I wonder what the difference is between this heat and the amount of heat generated by pumping the fuel over a relief valve at 60 psi continuously. The heat is generated at both the pump and the valve, to say nothing about the longevity of the pump.....
The pump only draws a few amps, it can't make that much heat compared to the motor.

As I said, virtually every car made in the last 15 years has a non-return fuel system. The effect on evaporative emissions is very significant to OEMs.

--Ian
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Old 08-18-2015, 09:57 PM   #55
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Evening gents.

It's been a while since I've been on MT, and even longer since I did this mod.

It works, I haven't had any issues at all with this setup. I figured I'd upgrade things as they failed, but so far so good. I did notice that the walbro-190hp pretty much puts out 55-60psi minimum. I am unable to turn down the afpr below that so the fpr on the rail is open all the time, allowing the afpr to run the show.
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Old 08-19-2015, 12:05 AM   #56
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I did notice that the walbro-190hp pretty much puts out 55-60psi minimum.
That probably means the 1/4" evap line is too restrictive and can't return all of the fuel at idle. If so, then it means your idle fuel pressure is not well regulated, and will vary with things like voltage and temperature of the pump.

--Ian
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Old 01-01-2016, 05:21 PM   #57
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Call me dense, but I CANNOT find a 5/16 -> 1/4 adapter fitting. Can someone please spoon feed me one?
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Old 01-01-2016, 07:57 PM   #58
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Call me dense, but I CANNOT find a 5/16 -> 1/4 adapter fitting. Can someone please spoon feed me one?
http://rapidswholesale.com/american-beverage-hose-union-5-16-x-1-4.html?gclid=CjwKEAiA5Ji0BRC5huTCyOTR3wISJACH4Bx4Q cEMSiJW16oyujAnF-fusjpEyHnXRNW9FGfUojqOFxoCAsHw_wcB
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Old 01-03-2016, 12:10 PM   #59
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Originally Posted by aidandj View Post
http://rapidswholesale.com/american-beverage-hose-union-5-16-x-1-4.html?gclid=CjwKEAiA5Ji0BRC5huTCyOTR3wISJACH4Bx4Q cEMSiJW16oyujAnF-fusjpEyHnXRNW9FGfUojqOFxoCAsHw_wcB
Thanks. I immedietly found one when I was looking for another size adapter on Jegs too. Just not my lucky day I suppose.

Going to tackle this today.
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Old 01-03-2016, 02:58 PM   #60
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You use a vacuume referenced FPR to MAINTAIN constant fuel pressure. For every 1lb of manifold pressure on a fixed pressure system the effective fuel pressure at the injector tip is reduced by 1lb. The same effect happens in vacuum. (Most OEM FPR's are 1:1)

The NB uses a returnless fuel system to comply with emissions standards.
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