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Old 04-14-2004, 02:30 AM   #46
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Quote:
Originally posted by V-One S
As i said would happen... Its to do with how long it takes the pressure to get to the tank... longer line, longer time... shorter line, shorter time...
Interesting, but it doesn't establish anything. On that basis it would be prudent to always use a short line to ensure sufficient pressure under all circumstances.

From our experience, we use the same length of pressure line irrespective of track with no issue.

I'd suggest there may be some tuning issues mixed up in this, but they haven't been shown to be singularly pressure line issues.

If it works for you, that's great, but I'd be interested to see the science established.
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Old 04-14-2004, 02:30 AM   #47
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Quote:
Originally posted by rjl
Maybe the extra fuel line or volume just damps the pulses but the pressure at both ends tries it's best to be equal.
Actually i thought about it a little bit... Try this...


Take a candle, light it, place it 3Metres away, and take a long blow at it, note how long it takes for the flame to flicker from your breath...

Now move 1metre from it and blow again... notice how it is a lot shorter of a time...

So at 4inches, say it takes 1second from engine exhaust port, to reach the pressure line inlet ON THE TANK...
Now at 8inches of pipe, it takes 2 seconds...

So at 300rpm it is blowing 300times per minute so each blow takes 1second each (on 4inch line) now it wants 1ml of fuel say to run at 300rpm... then we accelerate and it wants say 2ml of fuel at 600rpm, now it takes 1 whole second of delay for the extra fuel PRESSURE to build up so it leans out for 1 second...

Now take it to 8inches, and at 300rpm, everything the same in fuel intake, blows per min etc... except it is going to take a whole 2 seconds to get the same amount of pressure up... so the engine leans out double the amount over those 2 seconds...
BUT you get a RICHENING effect on the longer line when slowing down heaps... so you jump on the throttle, and hey presto, because of longer line, you still had a higher pressure in the tank then with a shorter line, so it fueled up, and you have the immediate amount of fuel there...


You get my gist...
Shorter line, takes less time for pressure waves to hit tank and adjust pressure there...
Longer line takes longer, but when the pressure in exhaust is backed off... it takes longer time for the tank pressure to drop down because it takes so much longer to get BACK OUT the pressure line
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Old 04-14-2004, 02:52 AM   #48
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nitropimp, i also use mugen pressure chamber iand i´ve noticed at the winters04 that pressure chamber in keisuke fukada´s (mrx3 and mtx3), mike swauger´s (mrx3 and mtx3) and masao tanaka´s (mrx3) cars . And all of them are mounted the opposite way you do, the wide side at the entrance (exhaust) and the narrow towards the exit (fuel tank) . Here in spain we use that way also. hope this helps.
best regards from europe, this forum is great!
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Old 04-14-2004, 02:56 AM   #49
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Quote:
The extra length of fuel pressure line helps in a "Fuel Up" process...
In a car, you would hear your best setting is 14.7parts air to 1 part fuel...
That is actually only for emmisions...
12.5Parts air to 1 part fuel is best for PERFORMANCE,
Now we would usually tune for a 12.5-13parts air...
Now we all know air flows quicker then fuel...
That figure of 14.7 : 1 is called "stoichiometric ratio"

that would be great if our cars ran on unleaded fuel....

what I mean is, 14.7:1 is for petrol, 15.7:1 is for LPG and I'm pretty sure that for methanol (without nitro) it is about 6.5:1...

what I'm getting at is that there are very few "constants" when it comes to our little cars, you could have something as silly as extra vibrations getting transferred to the fuel tank which will aerate the fuel mix causing a leaner mixture, then your 8 inches or whatever may not be the same...

practise, practise, practise !

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Old 04-14-2004, 03:03 AM   #50
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14.7 is stoichiometric... yes... (i can never spell it, yet alone say it)
that is the PERFECT rate for EMMISIONS
Most people think that is the rate you want to obtain in an engine...
But for a car, when accelerating you actually want to drop to 12.5 for MAXIMUM torque... but you get a worse emmisions...
And for best fuel economy you want to get out to 15.4

(I know this because i have been talking to an engineer of a new ECU and he has been teaching me in theory how to set up and TUNE an EFI car with this ECU... and anyother one really)
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Old 04-14-2004, 03:53 AM   #51
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I understand what you are saying, but our situation is a little different I think.

. . . what about this, then.

Firstly, I don't think our little engines will even run at 300RPM, but 12,000RPM there are 200 pulses per second.

Think of the pipe/ pressure line/ tank as one pressureised system.

How much fuel is moved to the engine between one pulse and the next?
Assuming the engine averages 12,000RPM and lasts 5 minutes on 75cc of fuel, the answer is .000125cc's. - not much.

Given that only a poofteenth of fuel is moved between pulses there can only be a poofteenth of air that's going to take it's place. There is no situation where any appreciable amount of air get's moved any significant distance down a pressure line.
The exhaust system essentially maintains pressure at the nipple.

Given that there are so many pulses per second, we may as well consider the pressure situation as linear, I reckon.
Acoustically, I'd expect the pulses to be well damped, firstly by the flexible nature of the sidewalls of the pressure line, their low energy, having been reduced to flow through the narrow internals of this line, and finally by encountering a relatively large volume of air in the tank. There is also the negative pulses to consider and wheather the whole acoustic thing loses the plot above the speed of sound.
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Old 04-14-2004, 03:59 AM   #52
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Well i can see what your saying... quite well too...

Basically the fuel pressure line acts to "power" our "fuel pump" as it would be...
But yeah, i forgot that sound moves at approx 330m/s... hmm... makes 2inches seem nothing...

Has to be something more about it, because there IS a notable difference to be had when changing lengths of pipe, and generally it can require an engine retune...

Must be another one of those Back Pressure Myths (exhaust back pressure)
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Old 04-14-2004, 04:44 AM   #53
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Yes, personally I view the pressure line thing as an old wives tale till some one shows me some hard science.

How about this.
How many cars are out there with "iffy' fuel tanks?
What about increasing the diameter of the pressure nipple and the line.
What about an ever so slightly non air tight tank?
As Sp Racer said, it could be aerated fuel from a ridgidly mounted tank.
It could be an NTC3 tank.

I just wonder how many people that find the answer in a pressure line change are actually missing the real problem altogether. If you and orangbaligila have found it appropriate, that's great. I don't pretend to know the answer.

But the Back Pressure Myths aren't actually myths. The idea is to harness the sound pressure waves to extract tha remnants of exhaust gasses in a 4-stroke engine, and I believe, to stuff back some escaping unburned mixture in our little engines.
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Old 04-14-2004, 05:18 AM   #54
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Quote:
Originally posted by Taylor-Racing


But the Back Pressure Myths aren't actually myths. The idea is to harness the sound pressure waves to extract tha remnants of exhaust gasses in a 4-stroke engine, and I believe, to stuff back some escaping unburned mixture in our little engines.
ROFLMAO... Okay, sorry, I'll quit laughing...
Directing you to a good little link, quite knowledgable link too, my main hang out area...

Here

Its a very good read, and answers a lot of stuff on the back pressure myth...
The only thing they have to stop now is the burning out of the exhaust valve with no exhaust... and remove our DB laws in Australia...
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Old 04-14-2004, 05:43 AM   #55
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My apologies - your talking about back pressure and that's a little different.
I should have said I was talking about acoustics.

. . . like this stuff.

The next topic might be about how to apply it to the intake side of things.
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Old 04-14-2004, 05:48 AM   #56
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Quote:
Originally posted by Taylor-Racing
My apologies - your talking about back pressure and that's a little different.
I should have said I was talking about acoustics.

. . . like this stuff.

The next topic might be about how to apply it to the intake side of things.
Sorry about that, Thats why i put the (exhaust back pressure) thing up behind the *another back pressure myth*, because you mentioned 4strokes and stuff to do with cramming it back in...
But on a 4 stroke there is nothing to cram back in except bad air (engine hasnt started to accept fresh air/fuel from intake yet)

I guess we keep confusing each other...

ill have a look at that acoustics stuff, i was wondering what it was...

have to check it out next week though, im going on holidays...
Be back about monday...
Cya all
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Old 04-14-2004, 06:03 AM   #57
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As I said:
"The idea is to harness the sound pressure waves to extract tha remnants of exhaust gasses in a 4-stroke engine, and I believe, to stuff back some escaping unburned mixture in our little engines. "

We use the acoustics on a two stroke for a different effect than a four stroke.

On a four stroke the inlet valve is opening as the exhaust valve is closing - it's referred to as overlap. The theory is that a negative wave will extract the remnants of the exhaust gasses as the piston slows on nearing TDC on the exhaust stroke. If it happens to pull some fuel into the exhaust in the process, who cares. We're talking about race engines here, but even cooking engines have overlap.
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Old 04-14-2004, 06:19 AM   #58
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Open the throttle, engine goes vroooom, if your engine goes well with extra pressure line it's all good, I just want a slight head at the carby and the engine goes really good. Vroooom. By the way there is a region of low pressure in the ventury that draws the fuel in and is a part of the equation too.
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Old 04-14-2004, 06:30 AM   #59
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Yes.
So what is the ideal length for the inlet tract that would coincide with the tuned pipe?
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Old 04-14-2004, 06:41 AM   #60
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3.14 with 5.5 mm venturi. Now give me some pie.
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