DIY Dual Feed
 

How many of you running a turbo performed this modification. I will be getting my injectors back from witchhunter back early next week and I want to drop them in for some N/A tuning. What I really dont want to do is remove the entire fuel rail to drill and tap.

How necessary is this modification, who done it? I know its a cheap insurance policy but I dunno if its worth the hassle.


P.S. I know your thoughts Chad.

I say do it. The theory is sound, and it's cheap and easy. Plus you can paint your ugly fuel rail. Mine's black.

My fuel rail was painted gunmetal... it looks awesome..and it took me like 15 minutes.

i will be doing mine, why not, its cheap, reasonable, and it gives some extra protection...

I am not gonna paint my fuel rail. Unless that has some sort of measurable benefits.

It lowered the FP of my 255hp to stock levels i say go for it you have nothing to lose.

Sam, would you please point me to any previous thread explaining this mod?

Thanks,

Rafa

I think it would be pretty foolish not to do it.

I did it before I went turbo and I've had no problems.

https://www.miataturbo.net/forum/showthread.php?t=10993 hey i am not sam but here is the right up very simple.

Cheap, easy, can potentially save your engine...Cheap...easy...

Thanks Magna. BTW how is the T/A coming? I scanned a pic of my 73 at the office. I'll see if I can send it to you today.

Regards,

Rafa

Cool i finished my new rear control arms now all i need is paint and an alignment. Depending on the alignment the paint will either be good for it is all straight or OK for alignment is pretty sketchy. ;) I would love to see pics BTW. hopefully i will post some to you soon as well.

Alright you guys sold me.

This may help:
https://www.miataturbo.net/forum/showthread.php?t=4948
https://www.miataturbo.net/forum/showthread.php?t=9645
https://www.miataturbo.net/forum/showthread.php?t=9645

I tried to pm you a pic from my office but had to give up on the effort. I don't know how to attach pics on pms. :mad::mad::mad:

Coño esta mierda de las nuevas tecnologías me tiene harto. Coño!

Good info in those threads. Thanks.

I have but one question. I was thinking of pulling the fuse for the fuel pump and turning the engine over to get as much fuel out of the lines as possible. The How To does not say to do it, but I figure its a smart idea. Yay or Nay?

not much fuel there if you open the gas cap it relieves all the pressure, what you are describing is overkill

Pulling the fuse is a good way to do that. I pull the fuel-inj fuse in the engine bay and crank it till i think it's good. Same deal for when i do fuel filters.

Unnecessary. A little fuel spilling over there will just serve to clean anything on that side of the engine bay... we're only talking about a shot-glass full at most of you pull the fuel cap. Have a towell on stand-by if you must.

I'll be doing mine this weekend, yay 4-day!

sweet, thanks for bringing this up again. i remember seeing this way back when i first got my car, but now that i have the turbo kit on order i am looking for excuses to work on my car until the turbo kit gets here.

Does any of this relate to NB's at all? We don't have the regulator sucking on the far end of the rail (though I doubt that's an issue).....

Also, I've taken out my pulse dampers. I should look at all that again now I guess.... Anyway, curious what the NB crowd does.

It was so easy to do, I don't see a reason not to. I would recommend putting an old blanket under the car when you do this so if you drop your plastic spacers they are easier to find. Mine bounced off the cement and rolled into the grass when I dropped it, took me a while to find it.

what's the concensus on power/boost level that this is required? I'm at 9psi right now, but when my clutch and DP come in I want to go to 12 psi this month. With my T3 that should be about 220Whp, maybe more. Think it's really necessary?

I would say everyone should do it. Anything to make sure all 4 cylinders get enough fuel should be done.

I'm not sure what rules apply, but it helps the #4 cylinder run cooler and not run lean.

I say do it. I didn't do mine, and while I've had no issues, I agree with Ben that the theory is good.

I haven't done it. No problems so far at up to 15psi. but then again I like to be pretty rich in boost - 12.5 at 4k tapering to about 11.8 at redline.

yeah, i'm running 12.5@8psi and plan to run 12.0 @12psi. should be safe, will still go dual feed eventually.

I was looking at brain's article and it says to use a 21/64" drill bit with the 1/8 tap. Am i missing something, 21/64 is much bigger than 1/8

1/8npt is not the same as 1/8. An npt is pipe thread and the 1/8" doesn't mean OD. Next time you're at Home Depot or something, go check out the npt stuff and you'll see.

ohhhhh, it all makes sense

To those of u wondering about difficulty...DO IT. Period. As far as the benefits I havent finished the car yet, but as far as experience needed/do i want to mess with this....DEFINTELY

Print Brain's instructions/post, get exactly whats on the list(21/64bit is common to find, might already have one....the tap/fittings/etc Advanced sells them, and ge the bit there like i did), and do exactly what he writes, it IS that simple and newby-proof.

As for "do i wanna mess with the fuel system" jitters....Its nothing. Esp if u alread took ur injectors off, u did 70percent of the work. The lines just pull off, perfect example about the shotglass of fuel(shop towel under u is all u need, if that) and open the gascap first. I wrapped a shop towel around a pair of lock pliers, and pinched the line to be extra safe. Make sure u dont lose the plastic spacers under the 3 bolts, wont go on the same without them(but they can be bought), and be gentle and patient with the clips on the injectors(which u already did).

Finally JB weld is like peanut butter and jelly, but thicker. U take a piece of cardboard, or a plastic knife and u spread it kinda. It hardens and seals, dunno how, magic maybe but it does...

And thats it, cheap insurance is the way I saw it, and I did the SAME thing and sent my injectors out, then wondered...hmmm should I?
Do it...

Guhh I guess I should do this before I go to 12psi.

Okay, so i have my fuel rail off, which was a bit harder than i expected, but then again, i'd never done it before. Anyway, i see how in brain's post it says to be careful not to lose the spacer. Well, i think i have lost the spacer. I have been looking for it for a while now and no luck. Is that something i can pick up at autozone or something? I know, i know, im a dumbass.
Thanks in advance.

What does the spacer look like and where is it, so I can anticipate it.

The spacer is a black plastic washer that sits in the intake manifold to space the fuel rail to the right height. They're about 1/8" thick or somewhere around there. Be careful, is spent 30 minutes looking for one i dropped. It was lodged between my oil pan and subframe, could hardly see it.

Yea but where is it? At the bolt points?

I ran without those spacers for a while. Just don't tighten the rail bolts down too hard upon re-installation.

'tween the rail and the motor, at the bosses for the bolts.

Im sure u could find the spacer at either Autozone, if not Mazda...
I would take a real good look tho, like posted above they tend to get invisble when on the subframe..
Did u hear it hit the floor? Or just rattle down? Check for it...worse case u could prob run w/ just 2, 1 on each end and dont tighten the middle bolt too much...

Have u started the actual mod yet? after rail is off it should only take like 15min with the right tools, plus jbweld curing time...

My question is, does anyone have hard evidence/facts to back up that there is a benefit from doing this. Theory aside, I have yet to see proof this helps anything on a boosted engine. I talked to Corky Bell about it a while back, and he says way back when, he did a bunch of actual bench testing on the fuel rail for the Miata, and found that making it dual feed didn't do anything at all, hence why he doesn't market a product like this. This seems more like a fashion trend as "everyone is doing it", but have no evidence to prove its real benefits.

^ exactly what I have been thinking. I am not an expert in fuel systems. But I dont understand the purpose of this mod if its a pressurized rail, it shouldnt matter that fuel flows from both ends or not. Especially if the fuel return is right where the second inlet would be.

^True... but it's $3 and about 20 minutes to do it... so if there is a benefit, even miniscule... it's good to follow the masses.

If there isn't a benefit, you're out nothing.

You ever heard of the term "reinventing the wheel"?

The only time I would imagine a dual feed would be most beneficial is when you are running so much fuel out of your injectors that you cant maintain adequate fuel pressure.

edit: shoulda made this thread a poll.

edit 2: I am just a student in all of this. My goal is to question everything until I have a complete understanding of it. Conversely I also dont like doing extra things I don't need until i know there is a definitive benefit in it.

yeah, i already have the fitting installed and i am getting ready to apply the jb weld. I will probably just put the two spacers that i have on the outsides and maybe put some washers in place of the missing spacer.

:bigtu:

As said above, $3, 20minutes = why not...
Im a newby, theory makes common sense to me, costs nothing, could be seen as added insurance if nothing else, and a chance to do simple diy project..if nothing else, look at what fm sells theirs for and feel good that u did it with $3!
Anyway, sounds like u did fine except for the spacer, and u have ur solution.. Make sure u replace the lines as they were and dont mix them up.. Im a nerd, so i put a piece of tape on 1 line and another on the corresponding hardline just in case, but really not needed if ur not a burnout like me :confused:

ps-dont forget jb weld takes like 24hrs to cure i think, read the back of the tube

Yea, newbies just eat this stuff up and do it. Except it doesnt make sense. Price isnt the issue.

well, newbies (me included) may eat this up but hell, i had nothing better to do today and like he said, FM sells a dual feed fuel rail so im sure that it doesnt hurt anything.

Dollars to doughnuts, I'd bet the dual feed rail does indeed help keep pressure high in the rail under heavy load. I've read of people reporting that a DF rail is good for an appx 5% reduction of IJDC on cars over 200 whp.

Price isnt the only factor, just a bonus...and as a newby u tend to listen to those that have been there and are giving the advice...:bowdown:

Anyway are there any downsides to the mod? Or are u guys just saying it may not be neccessary? When I looked into doing it, i didnt see anyone talking about any issues in doing this....

There aren't any downsides unless you are just retarded and screw up drilling and tapping the end, thus spraying fuel all over your hot engine as it bursts into flames. With all the smoke, you can't see and end up driving off a 200 foot cliff, you come crashing down on your mom, everyone dies. The end.

FM are a bunch of capitalists, I would take anything they say with a grain of salt until I see facts to back up claims.

You're in the finance business, you know not to listen to anyone when it comes to where to invest your money, you do your own due diligence. Might be a bad example, but you gotta think for yourself and first prove to yourself that you believe in something before blindly following someone else.

Are there logs to prove this? Have people logged before conversion and after?

You're putting way to much time into a 5 minute mod Sam.

I tried doing this and my car hemorrhaged fuel all over my garage when I started it up. Mazda sells the spacers for el cheapo about $7?

I run a dual EGT gauge with sends in the manifold (BEGI type 5) about 1.5" away from turbo inlet, with one at cyl #1, other at cyl #4 side. There is typically a 50-100 degree delta between the two sends. For the record I see 1100-1200F at cruise at 70mph. 1100F at 60mph 1200 or so at 80mph, 1500 and rising on a good WOT 4th-5th gear pull :)

I am running stock fuel rail with 750cc injectors and 12psi w/ gt3071. I bought a FFS dual feed rail and will eventually set it up and see if the temps match up. If the Hydra could trim by injector i suppose this wouldn't be an issue but oh well.

100 degree difference between two sides of the manifold. Thats a big difference.;) :rolleyes:

Its principle.

Yes bad example about the financing, but I understand what ur saying...But I stated my reasons, my opinions & thats the way I went. No one seems to have any hard evidence either way, and theres no downsides to doing it, coupled with the fact that its being recommended not only by credible vendors who make money, but being recommended by experienced people who arent making a penny, or costing u a penny....

Unless someone can prove its actually bad in some way, then Ill take the word of the vets plus the theory..
Kinda like u guys are the prosecuters, and the mod is crim defense. Again, this is MY opinion, and nothing more...

Heres a question. Whats the size of the bore on our fuel rails?

If someone is really good with numbers and has time, you can figure out the pressure loss across the fuel rail using this.

http://www.efunda.com/formulae/fluid...e_friction.cfm