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Old 07-12-2012, 05:16 PM   #1
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Default High fuel pressure (7-8 bar) on ev14s better?

I have read many times over "ev14 based injectors love high pressure."

Do any of you run really high static fuel pressure with them?

I've read they provide better atomization at high pressures, but can't find anything else than people just saying that. I understand that bosch rates them at 8bar 120psi, but does anyone use it?

Does it provide lower egts?

Does it allow more timing advance?

Is there any actual real world benefit?

If so, what fuel pump setups allow for such high pressures?

I'd ike to hear how high pressure on these injectors changed your setup.
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Old 07-12-2012, 08:03 PM   #2
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Fuel pump wise you're almost certainly going to need 2 pumps in line. The one in the tank needs to be higher flow. All pumps do is create a pressure differential which makes fluid flow. So if the first pump increased the pressure from 1 bar (atm) to 4 bar a 1:4 pressure ratio, the 2nd pump would only need to have a 1:2 pressure ratio to get it up to 8 bar. The 2nd pump would only be doing as much work as it would take make 2 bar in your fuel rail. But this is with 1 bar in the intake manifold, if you wanted a 8 bar pressure differential and you were making 22 psi you would need 9.5 bar in the fuel rail. Which pumps to run? Cant say without knowing how much fuel you use.
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Old 07-12-2012, 08:55 PM   #3
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Well before getting into specifics on which pumps to get I'd like to see if anyone has actually had any benefit from doing this.

I mean it makes sense, but other than more fuel which I don't need, I'm curious if any of the other benefits are worth pursueing.

Higher mpg?
lower egts?
More detonation resistance?

Anything actually worth while? Is this just one of those things thats better on paper?
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Old 07-16-2012, 04:44 AM   #4
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ID says the injectors like 90psi of rail pressure at WOT. I run 70psi of base pressure.

I would expect a little bit more power and a small improvement in fuel economy based on better atomization and getting more of the fuel into the chamber and burnt (vs. in bigger droplets).

Twin pumps is totally unnecessary unless the words "500whp" and "E85" are included in the conversation. There are more than a couple of drop-in fuel pumps capable of moving big flow at mega pressure.
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Old 07-16-2012, 05:38 AM   #5
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Sav did you ever try them at Stock NA pressure?. My small understanding is that a higher base pressure will give a more linear operating range to the lowest end of the scale. hopfully resulting in better atomised and more consistant fuel delivery at low PW. Is that the general reason for raising the pressure, to try and sit in the "prime efficency range" of the injector so to speak?.
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Old 07-18-2012, 10:36 AM   #6
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Quote:
Originally Posted by Leafy View Post
Fuel pump wise you're almost certainly going to need 2 pumps in line. The one in the tank needs to be higher flow. All pumps do is create a pressure differential which makes fluid flow. So if the first pump increased the pressure from 1 bar (atm) to 4 bar a 1:4 pressure ratio, the 2nd pump would only need to have a 1:2 pressure ratio to get it up to 8 bar. The 2nd pump would only be doing as much work as it would take make 2 bar in your fuel rail. But this is with 1 bar in the intake manifold, if you wanted a 8 bar pressure differential and you were making 22 psi you would need 9.5 bar in the fuel rail. Which pumps to run? Cant say without knowing how much fuel you use.
Bunk!

HP requirement for a pump is defined by the DIFFERENCE in pressure, not the ratio. So to go from 1bar (atmospheric pressure) to 4bar (3bar over atmospheric pressure) requires the same pump power as going from 4bar to 7bar!

and for doubters, here is the formula:
P[kW] = Q[L/min] x P[bar] / Y

where Y is a factor for pump efficiency.
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Old 07-18-2012, 10:45 AM   #7
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you aren't disagreeing with anything I said. Yes with the same input pressure the power required for a change in output pressure will be the same magnitude no matter what the original input pressure was. But it's easier to take 4 bar input pressure and make it 8 bar than it is to take 1 bar input pressure and make it 4 bar.
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Old 07-18-2012, 10:52 AM   #8
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^Read it again. Try to understand.
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Old 07-18-2012, 11:29 AM   #9
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For the OP:
All nozzles will atomize better (make smaller droplets) at higher pressure. This is in direct correlation with mass-flow of course. The upper pressure limit for a given injector is AFAIK usually not determined by the ability to atomize, but by the ability of components to handle higher pressure. For example at too high pressure a valve may not be able to open at all- that would set a natural maximum for the pressure rating. There are also other effects like chatter etc. that might limit the pressure range.

So should we always crank the pressure to maximum allowed by the injector?

Well, no:
- At higher pressures, especially for large injectors, the opening times under low load get VERY small and hard to control
- operating anything at it's limit will increase it's probability to fail
- Atomization is only very important at low loads and idle. High load and boost don't really need good atomization.
- You quickly get to the point of diminishing returns. See graph below on droplet size


This is a graph of droplet size on agricultural spray nozzles at different pressures (and the resulting different flow rates). You can see that the change from 1bar to 2bar is significant, but the change from 2bar to 3bar is rather small. Nozzles will reach a point where atomization does not improve much with higher pressure, yet flow rates will still increase.

All that being said, Bosch does extensive research on their nozzles. So when they claim an operating pressure range for their injectors, we can be reasonably certain, that they will work very well anywhere in that range.

My suggestion: run at the lowest pressure that allows you a duty-cycle of 80% or below, as long as you meet minimum pressure requirements (not sure what those are on EV14s).

P.S.:
I understand that agricultural nozzles are not the same as fuel injectors. Those droplet sizes would be horrible for internal combustion engines. But they do work very well for pesticides. There are similar graphs for fuel injectors, but they are covered by confidentiality agreements.
If somebody wants to send me a pump, some hoses, a pressure regulator and a few injectors, I can take some laser diffraction measurements of the resulting droplet sizes. I will use water though- spraying fuel all over our warehouse or lab is not a great idea...
Attached Thumbnails
High fuel pressure (7-8 bar) on ev14s better?-nozzles.gif  

Last edited by stefanst; 07-18-2012 at 11:43 AM. Reason: Added more info
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Old 07-18-2012, 11:44 AM   #10
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I have a set of EV14 and they work better at 3 BAR as far as I'm told. Some people here have attempted to run them at 4 BAR and that's where they started vaporizing badly. I'm guessing it's not a matter of the injectors being EV14 but rather their nozzle and capacity.

I'll take the chance to ask this question though. How do you fit EV14s to a Miata? The fuel rail is for Denso-style 11mm injectors, and EV14s are Bosch-style with a 14mm mouth!
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Old 07-18-2012, 11:46 AM   #11
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Quote:
Originally Posted by stefanst View Post
^Read it again. Try to understand.
Had an error in my units, I was missing feet in the equal using mass flow. And this is why fluid and thermofluids were my only non-A's in engineering.

I still say that you won't find a fuel pump that will make that pressure in one stage easily.
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Old 07-18-2012, 11:51 AM   #12
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Quote:
Originally Posted by ThunderFox View Post
...I'll take the chance to ask this question though. How do you fit EV14s to a Miata? The fuel rail is for Denso-style 11mm injectors, and EV14s are Bosch-style with a 14mm mouth!
I have a set of these on order. EV14 injectors
My assumption was they're properly modified. Now you have me worried....
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Old 07-18-2012, 11:54 AM   #13
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Those are indeed EV14s and they seem to have some sort of "cap" to adapt them from 14mm to 11mm!

I wonder if they sell those caps separately!
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Old 07-18-2012, 12:13 PM   #14
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Yup, adapters. And yes, many companies (like T1Racedevelopment) sell the caps seperately
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Old 07-18-2012, 12:40 PM   #15
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Quote:
Originally Posted by Leafy View Post
...I still say that you won't find a fuel pump that will make that pressure in one stage easily.
Base values:
BSFC BP Engine (worst case): 320 g/(kWh)
Density gasoline: 720 g/l

So we need approx. 0.44l/(kWh)

The Walbro "high pressure" 190 ltr/hr pump delivers 22gph at 120psi. Or approx. 80lph at 8bar
See Fuel Pump Specs

This means that a standard Walbro pump can support 180kw at 8bar. That's approx 250hp.

Now a lot of these values are estimated, but I don't see any problems making 200+ hp on a standard pump at 8bar.
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Old 07-18-2012, 12:43 PM   #16
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Out of sheer curiosity, how much would you be able to pull out of a 1.6 stock engine on stock injectors and stock pressure (basically stock everything + turbo) without the injectors going over 80% duty cycle?
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Old 07-18-2012, 12:58 PM   #17
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There's a convenient WIKI here answering your question:

Fuel Injectors - Miata Turbo FAQ
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