DuAl FeDe fewyl RaILS 4 da WIn?
06-02-2008, 07:23 PM
#1
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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.
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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06-02-2008, 07:49 PM
#4
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.
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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06-02-2008, 08:10 PM
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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.
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.
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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06-02-2008, 09:06 PM
#8
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...
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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06-02-2008, 09:10 PM
#9
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.
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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06-02-2008, 09:13 PM
#10
^^^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...
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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06-02-2008, 09:32 PM
#11
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
http://forum.miata.net/vb/showthread.php?t=15109
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06-02-2008, 09:33 PM
#12
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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06-02-2008, 09:49 PM
#13
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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.
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.
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.
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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06-02-2008, 10:10 PM
#14
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.
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 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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06-02-2008, 10:12 PM
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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.
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.
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06-02-2008, 10:30 PM
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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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06-03-2008, 12:01 AM
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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.
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?
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.
Yes, true that, good point. And of course, that's 43.5 differential...
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?
It occours to me that running four hoses from a far away mounting point is the way to go, some OEM's do it.
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.
Dual-feed rails aim to stabilize the pressure, which means you get less single-cylinder lean events and you can run more timing.
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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06-03-2008, 12:36 AM
#18
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...
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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