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Old 05-07-2015, 07:24 PM   #41
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Making **** up u say, all am saying is I never a saw a fuel pump replacement be it a stock one or uprated change the afr in any way, fuel regulators are a set rate and shouldn't go beyond that if the do there faulty, simple as that.
KEEP TALKING ****.
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Old 05-07-2015, 07:24 PM   #42
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Sometimes, a pump offering a different volume of flow will cause a regulator to meter differently simply because it is unable to handle the additional volume in the same manner. Therefore, a re-tune should be conducted to ensure proper fueling.

We try very diligently to keep incorrect information off of our forum. Please stop posting opinions that have no basis in fact.
Simple translation: see Concealer's post above.

And put ******* Ireland in your profile so people will know where you are located, please. We have other Irishmen here that are quite intelligent and helpful, so I am waiting for your spark of brilliance.
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Old 05-08-2015, 12:25 PM   #43
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Am sorry but in my eyes that's not incorrect info, if a fuel pressure regulator can't handle the pressure from a fuel pump then it would be time to uprated that then correct fuel table.
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Old 05-08-2015, 12:52 PM   #44
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You're thinking of a perfect world, where a FPR is bullet proof, and provides exactly 60psi of fuel no matter what the pump is doing behind it, and what the engine is doing past it. But cars aren't perfect.
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Old 05-08-2015, 12:54 PM   #45
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Quote:
Originally Posted by triple j View Post
Am sorry but in my eyes that's not incorrect info, if a fuel pressure regulator can't handle the pressure from a fuel pump then it would be time to uprated that then correct fuel table.
I have a question for you: how many miata's have you done fuel system upgrades and testing on?
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Old 05-08-2015, 01:13 PM   #46
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Not one, this is my first miata am working on, Nissan's Toyota's mainly, it is a good point but should the same principal apply.
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Old 05-08-2015, 01:19 PM   #47
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I thought so.

It's funny because we get a ton of Nissan guys that join the subaru forums too, and they act just like you, think that every car is the same because the basic principles are the same.

They're not.

That's why you see specialized shops, specialized tuners, specialized forums and communities. While some general basics apply accross the board to all cars, there are tons of little quirks and issues each has that is exclusive to that car. This is why you're catching a lot of hazing on this forum.
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Old 05-08-2015, 01:34 PM   #48
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Here is the thing. The regulator is an analog device. The pressure on the fuel side balances the air PLUS a spring on the other side. Any imbalance causes the diaphram / plunger to move, allowing the fuel to flow. The more flow through that valve, the greater the opening has to be to come to equilibrium. But, now the spring is compressed a little bit more, so the fuel pressure by definition must be greater than it was a low flow. The regulator is not perfect. In addition, the greater the flow in the bypass lines, the greater the pressure drop, increasing the fuel pressure a bit more. Hence, the greater the flow through the PR, the greater the fuel pressure.

Now, let's graph, simplistically with straight lines, this flow / pressure relationship of the PR, along with two fuel pumps. I think the pump curves need no explanation. Let's assume a condition, such as idle, where so much of the fuel that is pumped goes through the PR that we can ignore what goes into the engine; or pump flow = PR flow.



The OEM Operating Line crosses the PR Operating Line. That point will be the system operating point. Similarly, the A/M pump operating line crosses the PR operating line. That would be it's operating point. Note that the two Operating Points are not the same.

The higher capacity pump does not even need to "overwhelm" the PR, or drive it beyond its designed capacity, to cause this effect. The higher flow will always result in a higher pressure.

Hence the need for a re-tune.

That's how I see it. DNM
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Old 05-08-2015, 02:57 PM   #49
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OK so, am not going to argue with u guys as I joined this to learn from u, I will see for myself when I get there.
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Old 05-08-2015, 03:09 PM   #50
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Quote:
Originally Posted by triple j View Post
OK so, am not going to argue with u guys as I joined this to learn from u, I will see for myself when I get there.

Or you can learn without even needing to see for yourself. That's the beauty of this particular forum: There's no need for anything groundbreaking, and anything groundbreaking probably sucks. We've already done all the testing you could possibly think of for you.

In fact, there's a great opportunity for you to learn here in this thread.
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Old 05-08-2015, 03:55 PM   #51
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Very true, am looking forward to getting stuck in to work on my car and then I should have some real questions for u guys.
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Old 05-08-2015, 06:11 PM   #52
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Honestly, this has been a very informative thread. I did search for this subject before asking/posting...and hopefully it will answer questions in the future.
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Old 05-08-2015, 07:56 PM   #53
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Quote:
Originally Posted by DNMakinson View Post
Here is the thing. The regulator is an analog device. The pressure on the fuel side balances the air PLUS a spring on the other side. Any imbalance causes the diaphram / plunger to move, allowing the fuel to flow. The more flow through that valve, the greater the opening has to be to come to equilibrium. But, now the spring is compressed a little bit more, so the fuel pressure by definition must be greater than it was a low flow. The regulator is not perfect. In addition, the greater the flow in the bypass lines, the greater the pressure drop, increasing the fuel pressure a bit more. Hence, the greater the flow through the PR, the greater the fuel pressure.

Now, let's graph, simplistically with straight lines, this flow / pressure relationship of the PR, along with two fuel pumps. I think the pump curves need no explanation. Let's assume a condition, such as idle, where so much of the fuel that is pumped goes through the PR that we can ignore what goes into the engine; or pump flow = PR flow.



The OEM Operating Line crosses the PR Operating Line. That point will be the system operating point. Similarly, the A/M pump operating line crosses the PR operating line. That would be it's operating point. Note that the two Operating Points are not the same.

The higher capacity pump does not even need to "overwhelm" the PR, or drive it beyond its designed capacity, to cause this effect. The higher flow will always result in a higher pressure.

Hence the need for a re-tune.

That's how I see it. DNM
Your graph is wrong, but your explanation at the beginning is partially right.

The fuel pump does not supply pressure, it supplies FLOW. The system in front of it produces a restriction which creates the pressure.

On my '99, the stock regulator could bypass enough fuel at idle to keep fuel pressure constant and correct with the stock fuel pump.

With a turbo and stock fuel pump, the pump could not supply enough fuel at high loads so fuel pressure dropped.

With a Walbro 255HP installed, the stock regulator could NOT bypass enough fuel at idle to regulate the fuel pressure. Thus I got higher-than-normal fuel pressure at idle/low load. At higher loads fuel pressure went back down to normal and stayed normal.

If you had a well designed return style fuel system and your current fuel pump was "enough" that fuel pressure stayed constant under all conditions, putting a larger pump would not affect the tune so long as the well designed return style fuel system can still bleed off enough fuel that fuel pressure stayed constant under all conditions. In reality, miatas stock fuel systems are not designed to deal with larger fuel pumps.
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Old 05-08-2015, 09:58 PM   #54
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You do like to argue.

Here is a typical fuel pump curve:


Notice that as pressure rises, flow decreases. Conversely, as flow rises, pressure decreases. Causality is irrelevant. It will seek a single operating point.

For my purposes, I chose to reverse the abscissa and ordinate, but the simplified shape of the curve, either way, goes from upper left to lower right.

DNM
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Old 05-08-2015, 10:03 PM   #55
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Not arguing, pointing out what you posted isn't right. The second graph you just posted has nothing to do with either your first pic that was wrong, or the statements I made in post 53.
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Old 05-08-2015, 10:05 PM   #56
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All that second graph shows is the maximum flow the pump can supply at a given head pressure.
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Old 05-12-2015, 09:28 PM   #57
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I highly recommend logging fuel pressure (pretty easy to do with a 0.5-4.5v transducer), as it opens your eyes to just how unstable the pressure can be.

My OE pump died and I replaced it with a DW300. This overwhelmed the FPR and I think I messed up the diaphragm or something as now it is anywhere from 300kpa to 370kpa (relative to MAP) depending on mood.

I'm in the process of fitting an aftermarket regulator, I will post back with my findings.
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Old 05-13-2015, 09:48 AM   #58
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Quote:
Originally Posted by patsmx5 View Post
All that second graph shows is the maximum flow the pump can supply at a given head pressure.

The real question is: Who cares? We all know how pumps work, they aren't voodoo.
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