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View Full Version : Anyone know the stock FPR thread size or the fuel return tubing size?



alltracman78
09-02-2011, 02:49 PM
I need to replace the -AN adaptor on my fuel rail, and I want to get rid of the -AN return line.
Does anyone know for sure what the stock FPR thread is? 10 x 1.0?
And the fuel return tubing? 6mm?

I don't have one laying around at home, and I'm trying to not remove the lines from my car 'til I have the replacements in hand, so I would really appreciate it if someone that has easy access to these parts could check. Or if someone already knows. The sooner the better if that's possible.

Thanks :)

Hookecho
09-02-2011, 04:46 PM
Just measured my spare regulator and it is 10 X 1.0

Let me walk back down to the shop and measure the return line.

Hookecho
09-02-2011, 05:21 PM
Yeah, the return tubing is 6mm I.D.

Sang
09-02-2011, 05:40 PM
On the gen2 and gen3 fuel rails, both the inlet (feed) and outlet (fpr) is threaded for M12x1.25

alltracman78
09-02-2011, 05:49 PM
I actually need the outer diameter of the fuel return line. Should have clarified that, sorry. :P
I'm getting an -AN to barb fitting, need the same size barb as the return line.


Just measured my spare regulator and it is 10 X 1.0


On the gen2 and gen3 fuel rails, both the inlet (feed) and outlet (fpr) is threaded for M12x1.25

:blink:

temperacerguy
09-02-2011, 06:03 PM
Well, if the ID of the hose is 6mm, then the OD of the pipe itself is 6mm with maybe a 8mm nipple.

temperacerguy
09-02-2011, 06:08 PM
however small recomendation....

If you are going to be in there anyways.... cut the "nipple" off of the return line, then flare the return line to -4, and use a -4 flex line for your return.

I lost the SCC project MR2 to a fuel return line coming loose. I am very careful about fuel systems now.

Hookecho
09-02-2011, 06:44 PM
The outside diameter was 10mm.

Sang is right. The thread is 12 X 1.25. I picked up the wrong FPR by mistake. I went back down there and got the right one and threaded it into a fuel rail just to be sure.

Sorry Jeremy.

Sang
09-02-2011, 07:25 PM
I lost the SCC project MR2 to a fuel return line coming loose. I am very careful about fuel systems now.

Normally I'd agree with you that flared ends + using a proper swivel seal hose ends is the way to go, but for the drain line it really isn't needed. it is a non-pressurized line and just a means for the fuel to trickle back to the tank. You can use a pushlock barb'ed fitting + pushlok hose on the fpr side, then clamp the other end to the stock hardline and work just as well. Just have to make sure it is clamp securely and that there is enough slack in the line to flex with engine movement.

For a pressurized line like the fuel feed line, a flare + proper hose end trumps clamp on crap.

With that said: When I get around to buying my flaring tool, I plan to flare the hardline (both feed and drain on the mr2) to use properly sealing adapters. :)

alltracman78
09-02-2011, 07:31 PM
Is the OD of the metal tubing or the rubber hose 10mm?


Well, if the ID of the hose is 6mm, then the OD of the pipe itself is 6mm with maybe a 8mm nipple.
If the ID of the rubber hose is 6mm I have my answer.
If the ID of the metal tubing [I asked for the OD of the metal tubing] is 6mm, I don't have an answer yet. :)

I don't like -AN line very much. This car is my first experience with it, and it hasn't been that great. The only nice thing about it is it's verstility.
I've had multiple problems with it leaking [never at a fitting], and I really don't like having it clamped onto something.
I'm scrapping that part of it and using a barb off the fuel return, and running regular fuel hose. Much less likely to leak. And I can clamp it any way I want.
But thanks for the advice. :)

Sang
09-02-2011, 07:34 PM
The OD of the barb is the same as the ID of the hose. You shouldn't care about OD of barb at the bulge because it's purpose is to provide friction/clamping so the hose doesn't pop off. The same concept applied to IC pipes. If you're IC piping is 2.5" OD, then you buy a 2.5" ID couplers regardless of what the pipe measures at the bead.

Generally when someone tells you what a pipe measures, they are telling you OD. So 6mm is what was stated back in post #3 by hookecho. ID measurements are hardly ever given unless specifically asked for because wall thickness can significantly change the size given the same OD.

AN fittings are ridiculously easy to understand. The numbers are a measurement of a fraction in 16ths, thus -4 refers to a hose with the same nominal size as a 4/16" pipe (or 1/8). AN (or JIC) refers to how it seals. AN means that it has a 37* flare on the end. It seals by butting against another 37* flare.

temperacerguy
09-02-2011, 08:14 PM
Normally I'd agree with you that flared ends + using a proper swivel seal hose ends is the way to go, but for the drain line it really isn't needed. it is a non-pressurized line and just a means for the fuel to trickle back to the tank. You can use a pushlock barb'ed fitting + pushlok hose on the fpr side, then clamp the other end to the stock hardline and work just as well. Just have to make sure it is clamp securely and that there is enough slack in the line to flex with engine movement.

For a pressurized line like the fuel feed line, a flare + proper hose end trumps clamp on crap.

With that said: When I get around to buying my flaring tool, I plan to flare the hardline (both feed and drain on the mr2) to use properly sealing adapters. :)

It doesn't really "trickle" it should be a low pressure line, but there still is pressure. The flow through the line (before the engine is running) with a standard upgraded 255LPH walbro is.... 255lph as everything running to the regulator is returning to the fuel tank. With the twists and turns and bends of the hard line, the hard line itself provides a restriction causing there to be pressure in the line. The higher flow the pump, the more restriction the hard line causes, and the more pressure at that fitting.

With the SCC project MR2, we were running very large aftermarket fuel pumps, and even that short 3' of hard return line with only 2 bends in it caused enough restriction that the return line blew off the hard pipe spraying fuel all over the engine bay causing an explosion.

Hookecho
09-02-2011, 08:16 PM
The ID of the hose is 6mm. The OD of the hose is 10mm. The OD of the hose barb was also 6mm.

Sang
09-02-2011, 08:21 PM
If properly sized, the drain line should be of very very low pressure. Low enough that a clamped on hose is no problem. If one decided to go overkill with a huge weldon or some other large capacity pump, then the rest of the fuel system should be adjusted accordingly.

a 255lph walbro isn't goign to overpower the drain line. A secure clamp has proven to be enough for a -4 sized drain. And I only say this because it's a bitch to try and flare the hardline with everything still installed, not to mention most flaring kits are meant for thin walled aluminum, not steel or even a decently thick walled aluminum. The cheapest flaring kit that i've found to be of good quality and handle most jobs on automotive platforms is the ridgid 377. $100 is a hefty price for a one time job. If getting someone else to do it or removing the tank, you might as well just use a -6 bulkhead and be done with it.

temperacerguy
09-02-2011, 08:35 PM
I don't like -AN line very much. This car is my first experience with it, and it hasn't been that great. The only nice thing about it is it's verstility.
I've had multiple problems with it leaking [never at a fitting], and I really don't like having it clamped onto something.


Odd, I have never had a properly used AN hose leak, and I have used MILES of it. What brand of AN hose are you using, and where is it leaking?

I have used only quality AN hose/fittings in the past (Earls, Russel, Aeroquip, XRP), so perhaps it's the brand of hose that you're using, or how you're using it.

I have seen AN/Stainless braided hose used incorrectly a number of times, perhaps that's one of your problems.
SS braided(over rubber) hoses should not be used for oil transfer (unless rated for it)
SS braided hoses are NOT high temp hoses, they should not be used for Turbo feed/drain lines as the heat will cook/melt the inner liner over time
SS braided hoses are only as good as the hose->hose end assembly. I have seen people screw up end assembly after end assembly till the hose is too long because they don't know what they are doing. If you've never been shown how to assemble the hose by an old timer, then find someone to show you... it will make a world of difference and you won't have any cuts on your finger tips.

I have been wanting to try the ultra cheap "siliconeintake" AN hose/fittings, but have not had a project where I needed them lately. I'm kind of weary of them, but willing to give them a chance. They look like an earls speed-flex knock-off.

Also, AN hose should NEVER be clamped to a hard pipe.

temperacerguy
09-02-2011, 08:47 PM
If properly sized, the drain line should be of very very low pressure. Low enough that a clamped on hose is no problem. If one decided to go overkill with a huge weldon or some other large capacity pump, then the rest of the fuel system should be adjusted accordingly.

a 255lph walbro isn't goign to overpower the drain line. A secure clamp has proven to be enough for a -4 sized drain. And I only say this because it's a bitch to try and flare the hardline with everything still installed, not to mention most flaring kits are meant for thin walled aluminum, not steel or even a decently thick walled aluminum. The cheapest flaring kit that i've found to be of good quality and handle most jobs on automotive platforms is the ridgid 377. $100 is a hefty price for a one time job. If getting someone else to do it or removing the tank, you might as well just use a -6 bulkhead and be done with it.

The problem is: Most people don't talk about the return line, so they don't know what a "properly designed fuel system" really is. They slap on a high pressure fuel pump, and adapters from the factory lines and call it a day. I personally figure if you're going to go as far as he is going, he might as well do it right.

I have a whole selection of flaring tools. 37/45 degree, and double flaring tools. And you hit the nail on the head, I have the ridged 377 you mention. It works very well, even on thick wall stainless brake line that I bend/flare for turbo oil feed/drain lines.

I believe that there is never a "one time job" because somewhere down the line you are going to need that tool again. So you might as well invest in the good tool needed and do the job right this time, and the next.

alltracman78
09-03-2011, 11:44 PM
Thank you all for your help, I really appreciate it. :)

And thanks for all the hose/tubing info. I already know this stuff, but it should be helpful to someone. I think the confusion came from people not understanding specifically what I was looking for. No biggie. :)

As far as the -AN lines leaking, they leaked from the lines themselves, not the fittings/connections. I learned how to assemble them when they first leaked 2 years ago. I just have fuel running through them, away from heat sources and not rubbing on anything. The first hoses I have no clue what brand [they came with the car], but I replaced them with Summit brand hose.

The return line is currently an -AN line clamped to the metal tubing. That's why I want the barb, to get rid of that. The car came that way; pretty much everything these idiots touched they half assed/fucked up. I've been slowly fixing things as I got the chance.