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Nitro Tuning Guide: Ultimate Compilation Guide to tuning Nitro Engines.

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  • Nitro Tuning Guide: Ultimate Compilation Guide to tuning Nitro Engines.

    Litt info ang tuning av nitro motorer

    Er på engelsk , men di fleste kan da lese engelsk .


    Here is a great simple guide to tuning your rc motor. Everyone should print these out and stick them inside your pitbox or whatever.
    ( SE BILDE )

    Click image for larger version

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    Mid Range Needle Tuning & Information , aka the 3rd needle.

    The screw inside the slide body is really the low-end needle, and it plugs into the main jet, or so called mid range needle(the 'brass needle' in the opposite side, usually flush to the surface of the carb body) without obtruding completely to allow a little of fuel to pass when the needle plugs into it to allow the engine to idle.

    The dimensions of the jet, or mid range needle (brass needle), its position relative to the venturi, and the dimensions, ramps and shape of the low-end needle dictates the fuel curve of the carburetor (or how much fuel enters by each cfm of air drawn into the engine at a relative carb opening).

    At idle speed, the engine is controlled by the low-end needle and how much air pass into the engine via the position of the barrel. But when you start to move the barrel to allow to pass more air, in fact, you're moving too the low-end needle, allowing at the same time to pass more fuel too. The low end needle adjustment is critical, because the engine relies on this adjustment for its temperature control when idling in the infield of the race track. This is the point where the engine does 90% of its work. If the top speed of the engine is good and the engine runs hot, you should generally richen this valve. You should see smoke when you open the throttle at low speed.

    Depending at which opening of the barrel the jet (mid range needle) is totally uncovered, and the carburetor starts being mandated by the adjustment of the high-end needle, and how much fuel this last adjustment permits to pass, rather than being governed by the low-end needle, can be varied (and the power band of the engine too, but slightly) by screwing or unscrewing the jet (mid range needle) and readjusting the low-end needle. But be careful screwing the jet too further into the venturi can lead to mix and temperature problems (in fact, you're leaning the mid rpms, where the engine operates at partial opening of the carb, this can lead to problems and erratic operation) this is why on almost all the engine booklets warns you about to not touching this adjustment.

    The position of the jet, relative to the venturi also changes the position on where and how much the vortex of air that enters into the carb varies how finely is the fuel sprayed into the air that enters (fuel is converted into a mist for being burned, a drop, no matter how little is doesn't burn and can create many and serious problems). This last can lead up to a conrod breakage (common) or piston breakage (not common but seen some) due to hydro lock.




    Weather Makes a Difference!

    The atmospheric pressure, temperature and humidity all affect the density of the air. On a hot day, or at high altitude, or on a moist day, the air is less dense. A reduction in air density reduces the amount of oxygen available for combustion and therefore reduces the engine’s horsepower and torque. For tweaking the fuel/air mixture and compression ratio, the air density is the most important consideration.

    The Air Temperature should ideally be the temperature of the air that is going into the intake of the engine.

    The Absolute Pressure (also called actual pressure or station pressure) is the ambient air pressure.

    Relative Humidity is a measure of how much moisture is in the air compared to the amount of moisture that the air could hold at saturation. Relative humidity is a function of temperature and therefore changes as the temperature changes, even if the amount of moisture in the air remains constant.
    The air density is the actual weight of a given volume of air. This is a key parameter for engine tuning.

    Resuming:
    When the air density increases, you will need to richen the air-fuel mixture to compensate. When the air density decreases, you will need lean-out the air-fuel mixture to compensate.

    Use the following as a guide to correcting your setting when the weather changes:

    Air temperature: When the air temperature increases, the air density becomes lower. This will make the air-fuel mixture richer. You must lean the mixture to compensate for the lower air density. When the barometric pressure decreases, the opposite effect occurs.

    Humidity: When the percentage of humidity in the air increases, the engine draws in a lower percentage of oxygen during each revolution because the water molecules (humidity) take the place of oxygen molecules in a given volume of air. High humidity will make the air-fuel mixture richer, so you should lean the mixture.

    Altitude: In general, the higher the altitude the lower the air density. When driving at racetracks that are at high altitude, you should lean the mixture and increase the engine's compression ratio to compensate for the lower air density.

    This is a guide to help you understand the effects of air and how weather can change tuning. Allthough this is an important and true factor. Theres no big need to focus on whats going on if its confusing to you , this is for the more advanced user so use this if it helps. Otherwise the printable chart above is the best for referencing how to tune your motor.
    Last edited by xilian; 05-07-10, 13:30.
    Lars Erling Olsen 1981 Trondheim Losi 22-4 - Losi 22 2.0 - 2x Xray T4 16 - Sanwa M12


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