How to minimize tune changes as tank empties?
07-28-2011, 05:57 PM
#21
Howdy Y'all
What is the best way to mitigate that nasty effect we all know of and that creates material changes in our .21's tunes as the tank empties? You know the syndrom... to feel "right" for the last third of the tank, the mill has to be tuned a bit rich the first two thirds... tank after tank... perfectly repeatable (and not talking letting the mill cool between tanks, just refueling tank on tank on tank).
I was told it was a matter of pressure line volume as this is the only thing one can really think of that varies when the tank empties (more volume to fill => less pressure in there => pushing less juice in carb) but then again with a diameter of 1/10" it'd take meters of fuel line to "dilute" the tank emptying effect.
Are there any cool tricks you guys can share?
Thanks!
Paul
What is the best way to mitigate that nasty effect we all know of and that creates material changes in our .21's tunes as the tank empties? You know the syndrom... to feel "right" for the last third of the tank, the mill has to be tuned a bit rich the first two thirds... tank after tank... perfectly repeatable (and not talking letting the mill cool between tanks, just refueling tank on tank on tank).
I was told it was a matter of pressure line volume as this is the only thing one can really think of that varies when the tank empties (more volume to fill => less pressure in there => pushing less juice in carb) but then again with a diameter of 1/10" it'd take meters of fuel line to "dilute" the tank emptying effect.
Are there any cool tricks you guys can share?
Thanks!
Paul
found it, wow 2008:
http://www.rctech.net/forum/nitro-of...ssure-mod.html
07-28-2011, 06:05 PM
#22
massimo fantini back pressure mod, had a mod he did onroad with a pressure line needle tune, i tried it a while ago but not long enough to try to race it or test tuning changes. i think that was his best option at the time and he swore by it.
found it, wow 2008:
http://www.rctech.net/forum/nitro-of...ssure-mod.html
found it, wow 2008:
http://www.rctech.net/forum/nitro-of...ssure-mod.html
http://www.jonehrc.com/2008/07/23/ba...the-euro-2008/
07-28-2011, 07:14 PM
#24
I haven't heard the results, but some people have been using the Cline or Ironworks fuel regulators. Muffler pressure is used instead of crankcase pressure.
http://www.ironbaymodelcompany.com/i...es/Page438.htm
http://www.ironbaymodelcompany.com/i...es/Page438.htm
07-29-2011, 02:06 AM
#25
The effect is caused by this:
Full tank = little volume to pressurize (just the pressure tube and the small space in the lid. As the tank empties the volume to pressurize gets bigger and bigger (pressure tube and a growing part of the tank) This causes a lower overall pressure (same pressure being applied from pipe but a bigger volume) = less fuel being pushed into the carb = leaner setting. Some tanks are better then others but even Kyosho has it to some extend when you pay attention. You can also see it by the temperature: when the tank is almost empty your engine temps will be higher. Fill it up again and temps go down a bit again.
Best way is to tune with a half full tank: a compromise between the 2 extremes (full/empty).
Full tank = little volume to pressurize (just the pressure tube and the small space in the lid. As the tank empties the volume to pressurize gets bigger and bigger (pressure tube and a growing part of the tank) This causes a lower overall pressure (same pressure being applied from pipe but a bigger volume) = less fuel being pushed into the carb = leaner setting. Some tanks are better then others but even Kyosho has it to some extend when you pay attention. You can also see it by the temperature: when the tank is almost empty your engine temps will be higher. Fill it up again and temps go down a bit again.
Best way is to tune with a half full tank: a compromise between the 2 extremes (full/empty).
Paul
07-29-2011, 03:01 AM
#27
Tech Master
Team Orion used to make a pressure regulator for the backpressure. You could adjust the pressure from the pipe, when the enigine wen`t to idle, you still had the high pressure in your tank. I liked the idea, bought one but never got aroaund to test it.
I have had experience with your problem before, but on the two times i have seen this, it is soemthing inside the high end needle blocking and opening the hole on the needleseat. This hacve happend at big races were my fueltank have been messured for volume. You can clearly see it when you take the high end needle out. It has a small silverline aroaund the needle, a scratch. flushed out with fuel and fixed the problem.
07-29-2011, 10:27 AM
#28
If you do mod your fuel tank lid to take more volume, your tank will be bigger as to volume and you will be over 125ml and you get a penalty according to rules... So, this might cure your problem, but will get you out of the race :-(
Team Orion used to make a pressure regulator for the backpressure. You could adjust the pressure from the pipe, when the enigine wen`t to idle, you still had the high pressure in your tank. I liked the idea, bought one but never got aroaund to test it.
I have had experience with your problem before, but on the two times i have seen this, it is soemthing inside the high end needle blocking and opening the hole on the needleseat. This hacve happend at big races were my fueltank have been messured for volume. You can clearly see it when you take the high end needle out. It has a small silverline aroaund the needle, a scratch. flushed out with fuel and fixed the problem.
Team Orion used to make a pressure regulator for the backpressure. You could adjust the pressure from the pipe, when the enigine wen`t to idle, you still had the high pressure in your tank. I liked the idea, bought one but never got aroaund to test it.
I have had experience with your problem before, but on the two times i have seen this, it is soemthing inside the high end needle blocking and opening the hole on the needleseat. This hacve happend at big races were my fueltank have been messured for volume. You can clearly see it when you take the high end needle out. It has a small silverline aroaund the needle, a scratch. flushed out with fuel and fixed the problem.
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