DuAl FeDe fewyl RaILS 4 da WIn?
06-03-2008, 12:53 AM
#22
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I'll go test it. If I can get the dyno time, I'll tune the spark map to max power on the single feed, swap over to a dual feed, and see if any additional timing gains me anything.
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06-03-2008, 01:09 AM
#24
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.
EDIT: Flow-benching wouldn't strictly be necessary, but would reveal a faulty or dirty injector that could skew the results; if it's not flowing well, it may flow more or less between tests. You could also do multiple tests, moving the position of the injectors on the rail, to also give more reliable results.
If there is a significant problem here to be discovered, I would think it'd be to the benefit of someone selling dual-feed rails to do A/B testing of their rail - particularly a custom milled piece, rather than a modified stock unit - but I'm sure there will be claims that this isn't necessarily a valid method... probably something about heat from the engine causing temporary swelling of the metal in specific areas.
Last edited by macker; 06-03-2008 at 01:15 AM. Reason: clarification
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06-03-2008, 01:52 AM
#25
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That thread claims that the fuel rail is fed from opposite ends when comparing the '90-'97 vs the '99+. Is this true? Has there been a trend of problems with particular cylinders in the '99+?
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06-03-2008, 01:27 PM
#33
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When you touch yourself, you make the baby jesus cry.
I like this. And I don't. From the other thread on m.net, there was a lot of talk about knock just from the rail. That's both convincing and unconvincing, leaving me undecided.
Yep, I don't think it would be too hard. I wonder if I can find someone with an extra rail. I've got my stock injectors around, I could test them. And I could borrow (or maybe use my 550's if I pull things apart) big injectors to see if the higher flow rates are an issue.
I will say that at stock injector sizes, I CAN'T see it being an issue, the OEM wouldn't do that.
And I think your edit is right. Anyway, it's pretty easy to match the injectors - and with the MS-II it's trivial to run them an exact amount - how much opening, how long, etc etc.
Well, a test with negative results wouldn't get reported. I'm not sure if someone has done it. The tinsy amount of testing I see in aftermarket automotive development shocks me.
Oh god, swelling from the heat? Inane. I could see heating the fuel, lowering it's density, that might be an issue. All I really need to do is find a extra head to bolt it all to, or make some clamps to hold the injectors in the rail.
And like $50 for gas, jesus that's getting expensive.
I dunno where you dinosaurs get your fuel. My 2000 feeds in the front.
I'm curious about that, from the m.net thread, supposedly some of the rails took more fuel, some less. There didn't seem a pattern.
Flowing more fuel just to flow it doesn't mean it's better. It kinda implies it is, but we're much more interested in eveness here.
I'd also be curious how linear the delivery is, perhaps what is even at low flow falls apart at the high end...
I wonder if I can come up with a more intelligent flow tester beyond just doing 100 squirts and weighing it.....
C'mon Joe, want to put on your director's hat? Good excuse to get tossed weekend after this?
You know, I was thinking the same exact thing... only difference being that you'd need to flow bench the injectors, to obtain a baseline, so you're not just measuring the difference in the injectors themselves. Also be interesting to see the performance under varying fuel pressures.
I will say that at stock injector sizes, I CAN'T see it being an issue, the OEM wouldn't do that.
And I think your edit is right. Anyway, it's pretty easy to match the injectors - and with the MS-II it's trivial to run them an exact amount - how much opening, how long, etc etc.
If there is a significant problem here to be discovered, I would think it'd be to the benefit of someone selling dual-feed rails to do A/B testing of their rail - particularly a custom milled piece, rather than a modified stock unit - but I'm sure there will be claims that this isn't necessarily a valid method... probably something about heat from the engine causing temporary swelling of the metal in specific areas.
Oh god, swelling from the heat? Inane. I could see heating the fuel, lowering it's density, that might be an issue. All I really need to do is find a extra head to bolt it all to, or make some clamps to hold the injectors in the rail.
And like $50 for gas, jesus that's getting expensive.
Here's the thread: http://forum.miata.net/vb/showthread...8&page=1&pp=25
That thread claims that the fuel rail is fed from opposite ends when comparing the '90-'97 vs the '99+. Is this true? Has there been a trend of problems with particular cylinders in the '99+?
That thread claims that the fuel rail is fed from opposite ends when comparing the '90-'97 vs the '99+. Is this true? Has there been a trend of problems with particular cylinders in the '99+?
Flowing more fuel just to flow it doesn't mean it's better. It kinda implies it is, but we're much more interested in eveness here.
I'd also be curious how linear the delivery is, perhaps what is even at low flow falls apart at the high end...
I wonder if I can come up with a more intelligent flow tester beyond just doing 100 squirts and weighing it.....
C'mon Joe, want to put on your director's hat? Good excuse to get tossed weekend after this?
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06-03-2008, 02:01 PM
#35
Actually Abe, the fuel rails on the 99-00 do feed through the back. On the front is a pressure dampener. If you examine it, youll see that the dampener on the front isnt really connected to anything. Instead of cylinder 4 running really hot, (like most cars) our cars have cylinder 1 burning up.
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06-03-2008, 02:22 PM
#38
I have no scientific data or any fancy way to say this so it makes sense to all of you, just a poor ESL guy here.
I am soley relying on common sense here. Every performance rail I have seen for FI cars has a dual feed. I have heared stories about the #4 lean condition from trusted sources and made my own conlusion. Those running sub 250whp don't need to worry about this, but lets be realistic. If you are pushing 300+ through a rail designed to be efficient at 102rwhp, is it worth the risk? We all know the damn formula, more air+more fuel=more powahz!!! Or something like that! I would hate to melt a piston in a built motor because I chose not to spend a couple hundred to make sure I am getting enough fuel across the board. If proper fueling is overkill, the why do we all not run AFPR and stock injectors?
I am soley relying on common sense here. Every performance rail I have seen for FI cars has a dual feed. I have heared stories about the #4 lean condition from trusted sources and made my own conlusion. Those running sub 250whp don't need to worry about this, but lets be realistic. If you are pushing 300+ through a rail designed to be efficient at 102rwhp, is it worth the risk? We all know the damn formula, more air+more fuel=more powahz!!! Or something like that! I would hate to melt a piston in a built motor because I chose not to spend a couple hundred to make sure I am getting enough fuel across the board. If proper fueling is overkill, the why do we all not run AFPR and stock injectors?
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