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Old 07-13-2010, 05:52 PM   #1
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Default Fuel line sizing.

Split from Savington's build thread.
https://www.miataturbo.net/media-53/absurdflow-tse-time-attack-miata-v-2010-upgrades-42276/



Quote:
Originally Posted by Savington
Finally found the time last night to fab up my fuel system. The rail is an AF piece, .500" ID, twin -6AN feeds and a single -6AN return. Fit and finish is flawless, obviously.

Injectors remain the same, ID1000s, the best money can buy. E85 compatible, unlike RC. Max rated pressure of 130psi, and they recommend 90psi for the best spray pattern, unlike RC (RC says 65-70psi max.) They will also idle at stoich due to the incredibly low, stable minimum times (0.8ms IIRC), unlike RC. These will literally idle better than an RC750 and probably even better than an RC550, despite being a SATURATED 1000cc injector.

Not taking any chances with fuel lines going soft, so the lines are Aeroquip -6AN PTFE, teflon internals rated for constant use with methanol/ethanol. It uses steel PTFE-specific fittings as well. Not cheap at nearly $12/ft, but the fuel lines are not a place you want to be skimping.

FPR is a Fuelabs piece, which is so nice we're going to start selling them. It's a one-in one-out, so no bottom port to block off like the Aeromotive A1000 unit. It's adjustable from 25-90psi, A1000 maxes out at 70psi base pressure. It also uses standard -6AN union fittings, not the retarded expensive ORB fittings. It's physically tiny as well, as you can see, which means it can get tucked back into the depths of the engine bay if you want. Fully E85 compatible, of course.

All that's left now is to reinstall the intake manifold, set base pressure, and fire it back up. My replacement tranny goes in this weekend, and hopefully I'll hit the dyno next week for some more oomph.





Sorry for the shitty pics, I promise I'll have some good ones this weekend. The car will be on display at MiataFest in Irvine on Saturday.
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Last edited by levnubhin; 07-19-2010 at 04:52 PM.
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Old 07-14-2010, 07:23 PM   #2
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Originally Posted by Rennkafer View Post
Why a -6AN back to the tank?? Normal practice would be a larger line on the return, in this case a -8AN.
First time I've ever heard that. I've always had good results with a larger feed and stock return.
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Old 07-14-2010, 07:25 PM   #3
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arent the hardlines the same ID?
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Old 07-14-2010, 08:04 PM   #4
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FWIW I am using the stock feed line and the stock return line on my 1994 LS1 Miata. I am flowing enough fuel for a guesstimated 350 BHP with good AFRs, verified with a WB02 sensor. I have an adjustable regulator holding it at whatever the LS1 rail pressure is, I think 53 psi IIRC. It works fine.
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Old 07-15-2010, 12:21 AM   #5
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Quote:
Originally Posted by ZX-Tex View Post
FWIW I am using the stock feed line and the stock return line on my 1994 LS1 Miata. I am flowing enough fuel for a guesstimated 350 BHP with good AFRs, verified with a WB02 sensor. I have an adjustable regulator holding it at whatever the LS1 rail pressure is, I think 53 psi IIRC. It works fine.
Sav will be running E85, so he needs more fuel flow.
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Old 07-15-2010, 12:59 AM   #6
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Originally Posted by Rennkafer View Post
Sav will be running E85, so he needs more fuel flow.
More flow isn't necessary if he simply adds pressure (which his injectors work best at). If it aint broke, don't fix it.
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Old 07-15-2010, 01:10 AM   #7
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I doubt he'll need any more flow than the ID1000's will provide. And I doubt he'll need more pressure than that afpr will provide.

I think he's set. Once everything is dialed in I want to see a video of him rowing through the gears. I'll bring a towel
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Old 07-15-2010, 01:20 AM   #8
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Quote:
Originally Posted by Trackwhore View Post
First time I've ever heard that. I've always had good results with a larger feed and stock return.
This is something we do on race cars regularly. The reason is that if you run the same size lines in/out then any flow restriction in the return line can act as an uncontrolled fuel pressure regulator. A larger return line gives you some overhead for "stuff" happening (like rocks/curbs/etc hitting the return line and restricting it).

My comment about needing more flow was meant to be as compared to the 350HP engine, which if it's running on straight gas needs less fuel flow than the same 350HP engine on E85.
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Old 07-16-2010, 04:09 AM   #9
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Quote:
Originally Posted by Rennkafer View Post
This is something we do on race cars regularly. The reason is that if you run the same size lines in/out then any flow restriction in the return line can act as an uncontrolled fuel pressure regulator. A larger return line gives you some overhead for "stuff" happening (like rocks/curbs/etc hitting the return line and restricting it).

My comment about needing more flow was meant to be as compared to the 350HP engine, which if it's running on straight gas needs less fuel flow than the same 350HP engine on E85.
A larger return line doesn't give you anything but a thinner wallet. If you want to prove otherwise, I'm all ears. If the pressure was so easy to control through size (or restriction) of a return fuel line, we could all simply run a smaller or larger size to set our fuel pressure and that's not the case. Sorry, I don't buy it.

Any car running E85 requires more fuel. This is common knowledge. You can compensate for flow with more pressure which is where the injectors have better atomization.

Use the stock return line. It's stronger than any replacement and it's already installed.

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Old 07-16-2010, 12:39 PM   #10
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Quote:
Originally Posted by Trackwhore View Post
A larger return line doesn't give you anything but a thinner wallet. If you want to prove otherwise, I'm all ears. If the pressure was so easy to control through size (or restriction) of a return fuel line, we could all simply run a smaller or larger size to set our fuel pressure and that's not the case. Sorry, I don't buy it.
And how exactly do you think the pressure regulator on the stock return line works? It's a variable restriction...

Quote:
Originally Posted by Trackwhore View Post
Any car running E85 requires more fuel. This is common knowledge. You can compensate for flow with more pressure which is where the injectors have better atomization.
Yay we agree...

Quote:
Originally Posted by Trackwhore View Post
Use the stock return line. It's stronger than any replacement and it's already installed.

He's already NOT running the stock return line... unless Mazda installed a -6AN line somewhere and hid it.
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Old 07-16-2010, 06:08 PM   #11
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I thought your focus was the return line, not the FPR? We all know how they work, and it has nothing to do with running either a larger or a smaller return line. Way to point out the obvious. Again.

Like I said, if you want to prove the usefulness of a larger return, I'm all ears, but telling me you run them on race cars isn't going to cut it. Being a **** doesn't help either.

My bad on the return line. I didn't know he already replaced it.
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Old 07-16-2010, 07:37 PM   #12
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Quote:
Originally Posted by Trackwhore View Post
Being a **** doesn't help either.
I dont want to point out the obvious... but...

Quote:
Originally Posted by Trackwhore View Post
A larger return line doesn't give you anything but a thinner wallet. If you want to prove otherwise, I'm all ears. If the pressure was so easy to control through size (or restriction) of a return fuel line, we could all simply run a smaller or larger size to set our fuel pressure and that's not the case. Sorry, I don't buy it.
So if changing the size of the return line doesn't affect fuel pressure at all, why is it there? Changing the size to zero or nearly zero (say .0001 inch diameter) is still changing the size, right? How much fuel pressure would you run with a .0001" fuel return?

It's pretty clear that you made up the part where anyone is trying to "control" the fuel pressure through return size. They're trying to PREVENT it from controlling fuel pressure. If the resistance of flow through the fuel return line is higher than the FPR, it's going to affect the pressure in the rail.

You want some proof?

Blow as hard as you can through your mouth with your mouth wide open and measure the pressure in your mouth.

Now blow as hard as you can with your mouth ALMOST entirely closed except for a tiny hole and measure the pressure in your mouth.

which is higher?

large orifice or small orifice?
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Old 07-16-2010, 08:35 PM   #13
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lol at oldschool **** talking morons.
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Old 07-16-2010, 10:53 PM   #14
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Quote:
Originally Posted by hustler View Post
lol at oldschool **** talking morons.
We all wish we were as good at it as you though...



I think Y8s covered in about as simple terms as possible why a larger return line is useful...
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Old 07-16-2010, 11:38 PM   #15
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Quote:
Originally Posted by Rennkafer View Post
We all wish we were as good at it as you though...



I think Y8s covered in about as simple terms as possible why a larger return line is useful...
But you missing the most basic part. The only reason to run a larger return is if your fuel pump, pushes more fuel per min then your motor is using AND you having issues getting the correct fuel pressure.

Now, I don't know at what point the stock miata hard fuel lines become an issues, but so far no one has had that issue yet.
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Old 07-17-2010, 12:55 AM   #16
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Originally Posted by wildfire0310 View Post
But you missing the most basic part. The only reason to run a larger return is if your fuel pump, pushes more fuel per min then your motor is using AND you having issues getting the correct fuel pressure.

Now, I don't know at what point the stock miata hard fuel lines become an issues, but so far no one has had that issue yet.
Go re-read the first part of post #149... there ARE reasons to do it other than what you describe in the particular case of a race car, which is what we're talking about. The OP has a race car in the 400whp neighborhood, running on E85... not a 200WHP street car running on pump gas.

For MOST applications I completely agree that anything other than the stock hard lines is unnecessary.
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Old 07-18-2010, 07:57 PM   #17
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are his fuel pump(s) pushing more than the stock hard line will allow?
if no then it is wasting money to upgrade the return.
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Old 07-18-2010, 08:05 PM   #18
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LMAO

I can't believe there's this much arguing and slap fighting over a fuel return line.

Lots of things Sav does on his car are to see if they make an improvement. He's testing lots of **** for his own knowledge and is kind enough to share some of that info with us.
Are some things he does unnecessary or not needed? Absolutely (imo). But without trying/testing **** we wouldn't learn anything new or evolve our methods.

His dyno plots, videos and feedback will be the determining factor.
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Old 07-18-2010, 08:26 PM   #19
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Quote:
Originally Posted by shlammed View Post
are his fuel pump(s) pushing more than the stock hard line will allow?
if no then it is wasting money to upgrade the return.
+1

Quote:
Originally Posted by Rennkafer View Post
Go re-read the first part of post #149... there ARE reasons to do it other than what you describe in the particular case of a race car, which is what we're talking about. The OP has a race car in the 400whp neighborhood, running on E85... not a 200WHP street car running on pump gas.

For MOST applications I completely agree that anything other than the stock hard lines is unnecessary.
wait.. the only reason is when the return line becomes restrictive, otherwise it not effecting fuel at all. I am not disagreeing on whether running a larger return in general is useful, I am saying that currently no one with a Miata has run into the return line being restrictive(or atleast hasn't spoken up about it). Even the LS guys have yet to voice any issues with the stock fuel lines.
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Old 07-19-2010, 02:21 AM   #20
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Quote:
Originally Posted by 18psi View Post
LMAO

I can't believe there's this much arguing and slap fighting over a fuel return line.

Lots of things Sav does on his car are to see if they make an improvement. He's testing lots of **** for his own knowledge and is kind enough to share some of that info with us.
Agreed... when I asked the original question (of Sav, btw), I had no idea nor interest in it turning into a pissing match. I'd still like to know what his thinking was on it, as that's now we learn things...
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