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How big is too big for fuel rail?


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I have an aluminum fuel rail extrusion that has an 11/16" ID that I would like to know if I can machine and use for my setup. The only question I have is if an 11/16" ID (1/2NPT) would be too large compared to the, I believe 3/8" ID or 1/4NPT, pallnet fuel rail?

 

Some specs of my car:

Megasquirt 2

L28ET (F54 block P90 head)

60mm TB

Walbro 255lph

Aeromotive fuel pump regulator

440cc injectors

Stock turbo (larger turbo and an intercooler not installed yet)

 

Sorry if this topic has been talked about already. I did try the search function here but I got thousand results about fuel rail but had a difficult time finding one out of the bunch about fuel rail sizing. Also, I accidentally posted this in another section that I shouldn’t of have… I can see how I can try to get rid of that one. 

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Yea that’s what I figured I would need to do. Which is not a problem because I already do that now. 

I’m just not sure for the amount of time the fuel pump is priming will be enough to have it be at the pressure it needs to be at before turning the key from ON to start. Either I have the pump run longer or turn the key twice to the ON position before starting it. I rather not have to worry about that if in fact 11/16” is too large. 
 

I do a lot of my own machining so I’m debating between purchasing the pallnet fuel rail for around $155 or purchasing the same size fuel rail extrusion and machining the injector holes myself for around $50. Or use the 11/16” fuel rail that I currently have.

 

z car depot actually sales fuel rails with a 1/2 NPT end which is basically what the 11/16” will be. That’s what’s throwing me off because there are two different through hole ID sizes that are offered for these motors and I’m not sure if both are ok to run. 

I also forgot to mention that I have a 3/8 feed line and a 5/16 return  line for the fuel. 

 

Just thinking out loud but would of course love some good feedback. 

Edited by mainboyd
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I had an old style Bosch adjustable regulator with hose barbs that I modified to have a vacuum reference.  Here is Bosch's modern version that already has a vacuum reference port.  Mine did not leak down.  It acted like a normal modern car FPR which does not leak down.

 

Edit - I'm not really sure how it's plumbed in to their system.  The flow happens between the O-rings.  But it might give you some ideas.

 

https://www.bosch-motorsport.com/content/downloads/Raceparts/en-GB/50154251144125323.html#/Tabs=50170635/

 

Edit further - actually they have an adapter.  If I had the money and was building a system from scratch I'd probably go with the Mini A and the adapter.  A person might think that priming the rail before every start is no big deal but being able to jump in and turn the key is much better.

 

https://www.bosch-motorsport.com/content/downloads/Raceparts/en-GB/50225163113309707.html

 

https://www.bosch-motorsport.com/content/downloads/Raceparts/en-GB/109952523.html

Edited by NewZed
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Has anyone heard of Pro Tunerz? They offer a fuel rail that looks to be the same size as mine.
https://protunerz.com/collections/frontpage/products/datsun-l-series-fuel-rail


Their prices are a lot better than everyone else’s on the market. 
 

They also offer, not their own, a FPR from Deatsch Werks. I emailed DW asking them if their FPR is capable of holding pressure when the fuel pump is not running after prime and if the car is off for a few days. I’ll follow up if they get back to me. 


I’m feeling a little more confident in the fuel rail size I currently have. Even though it’s on the larger size, I still think it will be ok with what you all have shared and what I have seen in the market from Z Car Depot and now Pro Tunerz. 

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I got confirmation back directly from Deatsch Werks. I asked them if their product holds pressure after the pump has primed the fuel and has turned off and/or if the car has been sitting for a day. They said, “I spoke with my Tech Staff, and it’s the check valve in your pump that maintains the pressure, probably for about a day, but it holds fluid in the lines indefinitely”

 

It makes me feel a little more confident in their product but not 100%. Maybe going the rout that NewZed shared would be the way to go. 

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3 hours ago, mainboyd said:

They said, “I spoke with my Tech Staff, and it’s the check valve in your pump that maintains the pressure, probably for about a day, but it holds fluid in the lines indefinitely”

 

That's a salesman who found out that it doesn't hold pressure so answered a question that you didn't ask instead.  "Fluid in the lines"?  C'mon.  "Tech staff" is probably one guy, maybe even the same guy you were talking to, switching hats.  All of those aftermarket companies use the same design, a ball-shaped valve in a large round seat. They just don't seal well.

 

I tried to find a price for those Bosch parts on the internet and they seem spendy.  And I only found a place in Australia that sells them.  But a call to the local Mini dealer might get better results.  Good luck.

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Here's an interesting thread.  It's funny how people who don't have the problem think they understand it better than people who do have the problem.  People are strange.

 

https://ls1tech.com/forums/fueling-injection/1830922-want-aftermarket-efi-regulator-holds-pressure-key-off.html

 

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1 hour ago, NewZed said:

 

That's a salesman who found out that it doesn't hold pressure so answered a question that you didn't ask instead.  "Fluid in the lines"?  C'mon.  "Tech staff" is probably one guy, maybe even the same guy you were talking to, switching hats.  All of those aftermarket companies use the same design, a ball-shaped valve in a large round seat. They just don't seal well.


Yea I noticed that too while posting it. I guess it’s foolish thinking to think the best of someone and simply take their word for it. At least in today’s world. 

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1 hour ago, NewZed said:

Here's an interesting thread.  It's funny how people who don't have the problem think they understand it better than people who do have the problem.  People are strange.

 

https://ls1tech.com/forums/fueling-injection/1830922-want-aftermarket-efi-regulator-holds-pressure-key-off.html

 

 

Yep I read that forum a couple days back when trying to figure all this out. I assume that’s why businesses selling aftermarket fuel rails offer an option for a cold start valve on the fuel rail?

 

Seems like there might not be an effective and cheaper way to fix this. Just going to have to crank a tad bit longer till it starts…

 

I’ll give it a little more thought but not too much because I want my z back on the road. 

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If you're using 440cc injectors you must have aftermarket engine management.  So you don't need an adjustable regulator.  I'm a big fan of factory designed parts, they're made to do things like hold pressure and last 100,000 miles.  I'd just find a 2.5 or 3 bar factory FPR and plumb it in.   Actually I'd go with the higher pressure to combat heat soak problems that the Z's tend to have. 

 

Example below. I don't know if that's 3 bar or not but the form seems right for what you're doing.

 

https://www.rockauto.com/en/catalog/bmw,1985,325e,2.7l+l6,1011643,fuel+&+air,fuel+injection+pressure+regulator,6124

 

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You make a good point about not needing a FPR if I already have a aftermarket engine management.
But how would the management system (I have MS2) regulate the fuel pressure on its own if the factory FPR is not adjustable? If I were to turn up the boost in the future then how would I make sure I have the ratio I am needing and know the factory FPR  is not restricting my flow?
I’m being honest here, I am no expert in this exact field of work. 

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There is a vacuum port on the FPR that increases or decreases fuel pressure based on intake manifold pressure.  The factory Nissan turbo system uses a simple FPR with a reference vacuum/pressure line.  It maintains a constant pressure so that the ECU can adjust injector flow rates accordingly.

 

Here's a description.

 

https://www.haltech.com/why-you-need-a-fuel-pressure-regulator/

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40 minutes ago, NewZed said:

There is a vacuum port on the FPR that increases or decreases fuel pressure based on intake manifold pressure.  The factory Nissan turbo system uses a simple FPR with a reference vacuum/pressure line.  It maintains a constant pressure so that the ECU can adjust injector flow rates accordingly.

 

Here's a description.

 

https://www.haltech.com/why-you-need-a-fuel-pressure-regulator/


Ok NewZed, that was a really good and clear explanation from that link! Nice find and thank you very much for sharing that.  
 

I guess the aftermarket FPR are another component in your build that you can use for fine tuning if necessary? 
 


Back to the drawing board and back to the OP. 
 

To answer the OP: Long story short, I should be fine with the 11/16” ID fuel rail. As long as I have adequate fuel pressure in the fuel rails. Which is mostly determined by the fuel pump and a good FPR. 
 

Second question, what’s a good FPR?: Basically, it’s a personal preference but can possibly be based on the build. If you want a FPR to hold pressure for longer than a few seconds or possibly a few days when the fuel pump is not running then a factory FPR is the way to go. A aftermarket engine management system will also help with the air:fuel ratio adjustment.

 

I guess that sums it up for the thread? Unless we can share what FPR are out there that would work best for the L-series engine with various hp ranges? Maybe that’s another new thread or something that has already been discussed in another thread. 
 

I can at least now go ahead and machine the fuel rail extrusion and start assembling. 

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