Mugen MBX6r thread

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mcdoogie
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Wed Jul 25, 2012 6:35 am

Gravity will always have an effect.... You just can't change the laws of physics. If the fuel level is higher than the carb inlet, there will be a positive suction pressure at the carb.... If it is lower there will be a negative suction pressure at the carb ( provided the fuel line is filled all the way). But in our case we are talking about such a small variance (say 60mm from full to empty) the total change due to gravity is insignificant. If you consider that typical atmospheric pressure sits around 1 bar or 100kpa, this equates to the equivalent of a column of water 10 meters high. So if you added 60mm to this as a worst case scenario the overall percentage of pressure change you are talking about a 0.6% pressure change.
In conclusion, I would be looking for something else to blame.

Therdrunner
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Wed Jul 25, 2012 8:33 am

Me Think You Boys Have To Much Time On Your Hands :lol: :lol: :lol:

ShaneA
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Wed Jul 25, 2012 12:21 pm

Yes Basil, quite day at the office yesterday :D . Nothing like a little physics and hydro dynamics to pass the time away :wink:

I totally agree Gray, gravity will always be there. What I was refering too was how having the fuel tank sealed or unsealed would make a difference in what the 1 bar of air pressure will do to the column of fuel in the tank. The example you have given is correct, as we do have outside air pressure entering the tank via the exhaust pipe and pressure line - so my refering to a fully sealed fuel tank is not a good practical example in this situation.
As you say, the .6% change in head pressure exerted by the standing column of fuel (between a full and an empty tank) is definitly too small to have any effect on what the boys are discussing here.
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zombie guy
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Wed Jul 25, 2012 1:59 pm

Just the thoughts of a Zombie,

1,The lid snapping shut on a low surface area of air (as it compresses also)would not create a fuel pressure spike from in tank pressure, as the pressure would go out the pressure signal line into the tuned pipe which is at low pressure when idle speeds occur (extra fuel would do the same by exiting out the pressure line) either way the fuel lines "spike" would be half of what is expected.If you are worried about Sir Issac Newtons discovery, gravity, then turn the fuel banjo fitting to face downward along with the run of fuel line.

2,Fuel on the exhaust header cooling it down enough to act like a "super heat sink" from the engine causing a change in tune, not likely as the quantity of fuel spilt would have to be pretty significant to achieve this.

This is the Zombie angle on it:
If a fuel stop takes more than 8-10 seconds (including the drive into the pit lane). The tune will alter due to the enhanced cooling that occurs inside SOME engines crankcases combined with the lower engine speeds.
Have you ever peed on hot rocks as a kid and noticed the amount of steam that pours off of them?
Combine this concept with low engine speeds and you might just have the lack of crankcase clearing/excessive fuel atomization and oil condensate ("case fogging" as I like to call it), then when you blip the throttle enough or "floor it" to take off, all that "fog" and oil condensate in the crankcase gets pumped up through the intake ports (in some engines these are a little too large in design for my liking) and into the combustion chamber in one massive sweep and "hello glow plug!".
I think in some scenarios this could possibly cause a glow plug (or spark plug on a petrol engine) fouling scenario?

HSN needle tuning would fix this in my opinion (as would many others sharing the same opinion).

kyoshoNZ
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Wed Jul 25, 2012 3:04 pm

Hey Guys

Wow, this discustion is diffenitly far more intellegent than the one rctech (y) , And i have to admitt, it goes way over my head :lol:

The only person I no that has been seriously affected by this tank (issue) is Peter Brimmer, It was fixed easily by putting on a long pressure tube, A splash gaurd and losening the tank, so even for you guys that dont think rb are right in their theory, there solutions work.

Im thinking that rb might no a thing or two about engines and tuned pipes and the fact that they have done some serious testing to resolve this issue leads me to beleive theyve got it right, it makes sense to me that if the high speed needle is resicting pressure at one outlet, when the tank is FILL and the lid is slamed shut the fuel will go out the other outlet, what I am unsure about is whether the pressure from the tuned pipe is enough to stop the fuel getting to the tuned pipe, but puting a long pressure tube das seem to be the fix, or not filling the tank right to the top is the guys in the states solution, but they have some funny ideas that make no sence as to what is causing it :lol: I guess the same thing could be said about me beliving in rb's theory :|

Cheers Mike

ShaneA
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Wed Jul 25, 2012 3:08 pm

Sounds logical Jim. The modern cooling heads are super efficient (sometimes too much so), and engines do cool rapidly at idle. Whether the crankcase would cool enough to cause sufficient lack of atomisation in such a short time frame is questionable, but the mixture could get rich enough to cause problems I guess, depending on the initial tune of the motor.

I always blip the throttle moderatly when getting refuelled and have never had this problem, so maybe clearing the engine out a few times over the short duration of the pit stop helps with what you have described, and keeps the crankcase free of any heavy droplet fuel build up that may cause problems ? Although having said that, the motor is running considerably leaner than normal with the tank lid open during refuelling anyway, so this would help to negate some of the crankcase build up too.

Hi Mike, we need something to keep us all amused in this crap weather :)
Last edited by ShaneA on Wed Jul 25, 2012 3:14 pm, edited 1 time in total.
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zombie guy
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Wed Jul 25, 2012 3:12 pm

Yes that is correct Mike, RB know a lot about RB engines.
By adding a LONGER signal line or fuel line is just like adding a restriction. This concept can also be used to control the fuel tank pressure Rise.
The pressure inside the tuned pipe at idle is at both a low pressure and frequency. Frequency of exhaust pulses controls how far a liquid or gas can move in any direction at any rate (velocity) determined by the pressure "driving" or acting on it. By adding length you are further reducing the effect of the pressure and frequency by adding a "restriction". It should work in theory and you have confirmed this with your testing 8)

As an engineer (Automotive) I learned never to disagree or tell someone they are wrong on their hypothesis. It is far better to conduct your own research and find a conclusion that works for your EXACT circumstances. I cannot therefore say you or anyone is wrong.

You are entitled to your belief Mike as you are most likely correct when it works for you on your given situation (y)


Shane I am not saying the cooling fins are doing the cooling but the fuel itself is doing the majority of the cooling as in the "peeing on hot rocks" example. This works when the fuel droplets change from a liquid into a gas ( how an aircon or heat exchanger works). It takes energy to make the physical change occur. In this instance heat energy.

Zombie

ShaneA
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Wed Jul 25, 2012 3:30 pm

I fully understand the latent heat of vapourisation stuff, that is how we put fires out using the huge amount of energy required to turn a fine water spray (with a huge surface area) into steam.
Would the fuel provide enough cooling in 8 seconds or so to drop the crankcase temperature enough - considering the motor will be coming in hot from running on empty, then running lean with tank lid open during refueling ?
Not disagreeing with the theory, just delving a little deeper 8)
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zombie guy
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Wed Jul 25, 2012 3:50 pm

Yes the fuel would in my opinion. The inner surface area of the .21-.28 crankcase is so small that methanol's ability to change its surface temps is very likely given the fact that the fuel also contains PEG oil (used in aircon as a temperature stable lubricant) found in most high quality fuels. This condensation layer of oil alone would see the sufficient heat sinking effect in this given criterion.

I can best explain this situation by quoting an except by G.J. Van Wylen and R.E. Sonntag :

"For quasistatic processes under constant pressure, ^H is equal to the change in the internal energy of the system, plus the work that the system has done on its surroundings.[1] This means that the change in enthalpy under such conditions is the heat absorbed (or released) by a chemical reaction. Enthalpies for chemical substances at constant pressure assume standard state; exactly 25 °C at 1 atmospheric pressure."

In the case of these internal combustion engines running methanol you will see multiplications of up to 62% of the above standard state environment.
This also proves true for different fuel formulation as well.

ShaneA
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Wed Jul 25, 2012 4:34 pm

Well its hard to argue with that :wink:
I will just keep blipping the gas at pit stops and hope it never happens to me :)

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Last edited by ShaneA on Thu Jul 26, 2012 10:54 am, edited 1 time in total.
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moonie
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Wed Jul 25, 2012 4:40 pm

zombie guy wrote:Yes the fuel would in my opinion. The inner surface area of the .21-.28 crankcase is so small that methanol's ability to change its surface temps is very likely given the fact that the fuel also contains PEG oil (used in aircon as a temperature stable lubricant) found in most high quality fuels. This condensation layer of oil alone would see the sufficient heat sinking effect in this given criterion.

I can best explain this situation by quoting an except by G.J. Van Wylen and R.E. Sonntag :

"For quasistatic processes under constant pressure, ^H is equal to the change in the internal energy of the system, plus the work that the system has done on its surroundings.[1] This means that the change in enthalpy under such conditions is the heat absorbed (or released) by a chemical reaction. Enthalpies for chemical substances at constant pressure assume standard state; exactly 25 °C at 1 atmospheric pressure."

In the case of these internal combustion engines running methanol you will see multiplications of up to 62% of the above standard state environment.
This also proves true for different fuel formulation as well.
Yeah thats what i thinking !! :D
Last edited by moonie on Wed Jul 25, 2012 4:49 pm, edited 1 time in total.

ChrisB
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Wed Jul 25, 2012 4:40 pm

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zombie guy
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Wed Jul 25, 2012 5:12 pm

Yup. On some days it can get worse :oops:

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trarena
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Wed Jul 25, 2012 5:21 pm

Apparently this option part solves any flameout issues on the MBX6R Shaneo - should be one available for the XB9 soon too if you keen!!!

Click Here

Mike.
www.rcparts.co.nz for Bittydesign, PTRC, AKA, Rapid Eyewear, BCE, Beta, APlus, KingHeadz

ShaneA
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Wed Jul 25, 2012 5:26 pm

Michael, Michael, Michael - how could you suggest such a thing. Im shocked and stunned :) :)



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