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Old 06-02-2008, 08:23 PM   #1
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Default DuAl FeDe fewyl RaILS 4 da WIn?

Seriously, what's up with that? I've heard lots of "it's so much better" but... what's the point? I'm never lean, I just use huge injectors.

Someone tell me what I'm missing. I like throwing money at my car as much as the rest of you, but can't I get gold rims to match my gold teeth instead of a bigger fuel rail?

I've got a 2000 with 550cc injectors, the stock returnless fuel system, and everything seems fine.
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Old 06-02-2008, 08:27 PM   #2
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The even distribution of fuel across all 4 cylinders.
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Old 06-02-2008, 08:32 PM   #3
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you're o2 sensor says you're never lean but it's taking an average all 4 cylinders, if you knew for sure that you have even fuel pressures across all cylinders it would just be more accurate and maybe more efficient
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Old 06-02-2008, 08:49 PM   #4
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There has been some research done that shows the injector at the opposite end of the rail from the single factory feed has the potential to receive slightly less pressure than the other injectors and run that cylinder a little lean. Lean=hot and guys were blaming their #4 piston failures on the stock single-feed fuel rail.

Dual feed costs $15 in parts... 2 fittings and about 2 feet of fuel line, plus a couple small hose clamps. There is absolutely no drawback to it and most guys say it eliminates one point of failure.
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Old 06-02-2008, 09:10 PM   #5
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Can't speak from experience here as I'm still N/A (here to learn, mostly) but if I remember way back when I took physics, liquids are not terribly compressible. The pressure at one end of the rail "should" be the same as the other. Further, the amount injected in a single pulse is very small relative to the total volume of the rail. I would think than any variation in fueling between cylinders would more likely be due to the flow rate of the individual injectors rather than any differences in pressure supplied to them.

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Originally Posted by samnavy View Post
Lean=hot and guys were blaming their #4 piston failures on the stock single-feed fuel rail.
More likely that #4 running hot is due to the inadequate flow pattern of the stock cooling system, IMO. But you're definitely right, a dual feed rail won't hurt anything either.
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Old 06-02-2008, 09:23 PM   #6
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that settles it, joe needs to drill and tap a fuel rail for a pressure sender over each injector and log the data....and of course video it!
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Old 06-02-2008, 09:29 PM   #7
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Quote:
Originally Posted by Mach929 View Post
that settles it, joe needs to drill and tap a fuel rail for a pressure sender over each injector and log the data....and of course video it!
+1. That's the only way to truly answer this "epic" question.
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Old 06-02-2008, 10:06 PM   #8
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i took the cant hurt anything approach...Have heard the same scary stories, and what Scottfw said makes ALOT of sense, but I didnt/dont have a definitive answer...
I was swapping injectors as most of us do, read Brain's writeup, and 15min later I had a dual feed...
So for 10bucks, as said above it cant hurt anything...and for the same 10bucks I know IF the stories are true I'm covered...so i can sleep well at night

Shiiiiit,wish all the decisions were this easy and cheap...
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Old 06-02-2008, 10:10 PM   #9
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Oh hell here we go again.

Ponder this. Injectors are designed to deliver their rated capacity down to a certain pressure ratio. That pressure ratio will never be that low anywhere in the rail, unless your fuel pump takes a **** which at that point your engine wont even run.

Dual feed rails are useless. Not even 1000hp supras run them with 1000 cc injectors.

Btw. Some guy on the m.net forums put four egt temp sensors in his stock exhaust manifold and noted only slight deltas on all the cylinders. Oh and number 4, was not the hottest.
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Old 06-02-2008, 10:13 PM   #10
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^^^I've actually seen a few of ur debates on this and you do make alot of good points, the logic is there....But when it was MY time to do it, I hadnt dug too deep..Like I said $10 and I wont have to worry...
Now had Scott not done that writeup, and I was considering an aftermarket dual feed, I prob would NOT have spent the money for that....

Anyway, interested to see which way this goes...
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Old 06-02-2008, 10:32 PM   #11
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Granted this was from a looooooooong time ago, but some "real world" testing on stock, dual feed stock, and Vishnu Performance dual feed rail. Draw your own conclusions.

http://forum.miata.net/vb/showthread.php?t=15109
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Old 06-02-2008, 10:33 PM   #12
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Who cares? You have to take the rail off to swap your injectors anyway. Just do it and dont worry about it.
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Old 06-02-2008, 10:49 PM   #13
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Quote:
Originally Posted by Mach929 View Post
you're o2 sensor says you're never lean but it's taking an average all 4 cylinders, if you knew for sure that you have even fuel pressures across all cylinders it would just be more accurate and maybe more efficient
So, make changes without diagnostics? Putting 4 EGT's would be good, putting 4 O2 meters would be better. THEN I'll buy it. With some way to trim it.


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Originally Posted by samnavy View Post
There has been some research done that shows the injector at the opposite end of the rail from the single factory feed has the potential to receive slightly less pressure than the other injectors and run that cylinder a little lean. Lean=hot and guys were blaming their #4 piston failures on the stock single-feed fuel rail.

Dual feed costs $15 in parts... 2 fittings and about 2 feet of fuel line, plus a couple small hose clamps. There is absolutely no drawback to it and most guys say it eliminates one point of failure.
It introduces points of failure, flakes of metal to clog injectors, fittings to fall out, hoses to break. Any engineering that went into the fuel rail at all is now shot by haphazzardly modifying it.

And people blaming one thing or another for their motor blowing up is pretty hard to prove. I got a flat tire, but had no dice on my mirror. And I only took them off that morning! It happened twice, so I'm convinced. I have 3 pairs of dice now. Number 4 runs hotter because the coolant doesn't go there.

I do think there's a lot to be said for pressure waves banging around in there, not that I'm sure dual feed would help. That's probably the reason injectors inject in the wierd order they do.

I'm not against it, but I'd like to seem more that says why I should. It's more complicated, soI want to see why it's better. Maybe a center feed would work. :-)

I gotta read that link.


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Originally Posted by levnubhin View Post
Who cares? You have to take the rail off to swap your injectors anyway. Just do it and dont worry about it.
My favorite arguement of all. GROUP BUY ON SENDING ABE $20!!! Yes, sending Abe $20 hardly costs anything and will buy you between 2-6%.

Please, send me the money. It doesn't cost a lot, so what they heck, just do it. It only takes 15 minutes.
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Old 06-02-2008, 11:10 PM   #14
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Quote:
Originally Posted by Saml01 View Post
Oh hell here we go again.

Ponder this. Injectors are designed to deliver their rated capacity down to a certain pressure ratio. That pressure ratio will never be that low anywhere in the rail, unless your fuel pump takes a **** which at that point your engine wont even run.

Dual feed rails are useless. Not even 1000hp supras run them with 1000 cc injectors.

Btw. Some guy on the m.net forums put four egt temp sensors in his stock exhaust manifold and noted only slight deltas on all the cylinders. Oh and number 4, was not the hottest.
I agree with you to some extent. I think the biggest problem with ours is the placement of the FPR. On most vehicles it is mounted at the end of the rail, ours is mounted between cylinder 3 & 4. So you have proper flow from 1-3 then out the FPR, but number 4 gets "stagnant flow" which means the pressure drop will be more significant. More so with larger injectors and higher RPMs.

I also fail to see the relevance of the NA EGT test. He wasn't making nearly enough power to be an adequate test for our application. Now, if he was making 250+ whp and rocking 460cc injectors at 7500 rpm... then it would be a worthy study.
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Old 06-02-2008, 11:12 PM   #15
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Quote:
Originally Posted by Saml01 View Post
Oh hell here we go again.

Ponder this. Injectors are designed to deliver their rated capacity down to a certain pressure ratio. That pressure ratio will never be that low anywhere in the rail, unless your fuel pump takes a **** which at that point your engine wont even run.
..what? Injectors are designed to deliver their rated capacity at one exact pressure, 43.5psi. Vary the pressure and you vary the amount of fuel delivered. Dual-feed rails aim to stabilize the pressure, which means you get less single-cylinder lean events and you can run more timing.
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Old 06-02-2008, 11:30 PM   #16
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Quote:
Originally Posted by Saml01 View Post
Dual feed rails are useless. Not even 1000hp supras run them with 1000 cc injectors.
You're a ******* retard. I wanted to be sure, so I called my friend who's actually in the middle of a 600whp Supra build right now. GT3582R, Full-Race manifold/DP, etc. Not only did he say that he is using a dual-feed rail, but he said that in all of his research into the fuel system for his car, he's never even seen an aftermarket single-feed rail for the Supra.

Come up with some legitimate evidence before sprouting off more of this anti-dualfeed ****. You got told over at M.net, and now you're getting told here.
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Old 06-03-2008, 01:01 AM   #17
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Wow, I'm glad I read that thread. It does seem pretty universally accepted the dual feeds are better than the single. I still think it's hard when you compare tuned dual feed to untuned single feed, and how is this dual feed accomplished?

It occours to me that running four hoses from a far away mounting point is the way to go, some OEM's do it.

Quote:
Originally Posted by Arkmage View Post
I agree with you to some extent. I think the biggest problem with ours is the placement of the FPR. On most vehicles it is mounted at the end of the rail, ours is mounted between cylinder 3 & 4. So you have proper flow from 1-3 then out the FPR, but number 4 gets "stagnant flow" which means the pressure drop will be more significant. More so with larger injectors and higher RPMs.
Oh really? Man, you NA guys have it rough. That's a huge problem. Not that I'm so sure the NB's have it better. I get the feeling your whole fuel system is just more marginal. Who upgrades their pumps in an NB because they outran it?

Quote:
I also fail to see the relevance of the NA EGT test. He wasn't making nearly enough power to be an adequate test for our application. Now, if he was making 250+ whp and rocking 460cc injectors at 7500 rpm... then it would be a worthy study.
Oh! I didn't know that... Yeah, that does invalidate it a whole lot. If it were THAT big an issue, Mazda would have caught it.


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Originally Posted by Savington View Post
..what? Injectors are designed to deliver their rated capacity at one exact pressure, 43.5psi.
Yes, true that, good point. And of course, that's 43.5 differential...

Quote:
Dual-feed rails aim to stabilize the pressure, which means you get less single-cylinder lean events and you can run more timing.
Aim to. Sure. But lots of engineering designs are "aimed" at doing something but truthfully don't do it at all or make it worse.

Really, I think to convince me, I'd hook up a rail (or set of rails), pressurize them with a stock pump, and run them 100 injections at a 75% duty cycle of 10 ms period (6,000 rpm equivilent) and see how much gasoline I get in each of four cups. If they are uneven, I would note it, and compare it to the other rail.

Everything else is pretty much a pissing contest?
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Old 06-03-2008, 01:36 AM   #18
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I think alot of people who are in the same position (not sure) do it as added precaution..
From what I've read it also seems like the more likely cause for #4 to go is the cooling system, but again for the cost of a DIY dual its a pretty easy decision..

As far as adding points of failure, if done correctly it seems like this is a null point...IF done correctly one shouldnt worry anymore than they would with single feed...

Ur right it'll always be a pissing contest till proper testing is done, but I've yet to hear a valid argument that doing this is a negative thing...Expensive, not needed, etc...but haven't heard about actual problems resulting from a dual feed...
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Old 06-03-2008, 01:39 AM   #19
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will someone please make one for my god damn 99 motor?
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Old 06-03-2008, 01:45 AM   #20
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^^^rotfl

I thought Zabac said his guy was doing both rails after all...said he found someone who lives close to the shop and was giving it in for mockup

Anyway, is it alot more complicated to DIY on a 99?
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