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Old 05-22-2009, 09:01 AM   #1
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Default 16% 20% 25% Nitro content???

so what are the signs of an engine(12 size) that runs on the above percentages?? i already know how a 16% sounds and tunes but how about 20% and 25%, how can i tell if an engine is using higher percentage(16%) of nitro. thank you any respond will be helpful.
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Old 05-22-2009, 11:32 AM   #2
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so what are the signs of an engine(12 size) that runs on the above percentages?? i already know how a 16% sounds and tunes but how about 20% and 25%, how can i tell if an engine is using higher percentage(16%) of nitro. thank you any respond will be helpful.
Nitromethane, commonly referred to as NITRO for short, is derived from propane. In itself, nitro is not even extremely flammable as one might think. The real power producing potential of nitromethane is that it carries additional oxygen with it into the combustion process. It acts as a fuel too, but the molecule carries oxygen along with it. In a way, nitromethane is sort of like a chemical "supercharger" for an engine. It helps get more oxygen into the engine to help burn more fuel and produce more power, but since the flame speed of Nitro is much slower than that of Methanol, adding Nitro the mixture slows the flame speed. This should not be a problem until you hit very high rpm’s. There's a moment where the engine cannot pickup more rpm’s because it needs to burn the mixture at much higher speed in the combustion chamber. 30% Nitro fuel also burns at a lower temp so it will give you advanced timing and therefore more low end power.
With lesser nitro, you may need to lean it a little more and your fuel mileage will be a little better, temps will vary and combustion chamber and carb setup need to be revised, but... more nitro doesn't necessarily mean more power, but yes more fuel consumption and less runtime for the same CC’s.
Higher nitro content does not cool the engine, in fact it creates more heat. Basically, more nitro = more oxidizer to the methanol which in turn creates higher combustion pressures which create more heat.
So more low end power, less runtime = higher Nitro contents
More high speed power, more runtime = less Nitro contents

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Old 05-22-2009, 11:48 AM   #3
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Nitromethane, commonly referred to as NITRO for short, is derived from propane. In itself, nitro is not even extremely flammable as one might think. The real power producing potential of nitromethane is that it carries additional oxygen with it into the combustion process. It acts as a fuel too, but the molecule carries oxygen along with it. In a way, nitromethane is sort of like a chemical "supercharger" for an engine. It helps get more oxygen into the engine to help burn more fuel and produce more power, but since the flame speed of Nitro is much slower than that of Methanol, adding Nitro the mixture slows the flame speed. This should not be a problem until you hit very high rpm’s. There's a moment where the engine cannot pickup more rpm’s because it needs to burn the mixture at much higher speed in the combustion chamber. 30% Nitro fuel also burns at a lower temp so it will give you advanced timing and therefore more low end power.
With lesser nitro, you may need to lean it a little more and your fuel mileage will be a little better, temps will vary and combustion chamber and carb setup need to be revised, but... more nitro doesn't necessarily mean more power, but yes more fuel consumption and less runtime for the same CC’s.
Higher nitro content does not cool the engine, in fact it creates more heat. Basically, more nitro = more oxidizer to the methanol which in turn creates higher combustion pressures which create more heat.
So more low end power, less runtime = higher Nitro contents
More high speed power, more runtime = less Nitro contents

AFM
Tomorrow I have big race.

I usually use 20% nitro, C7TF glow plug, for normal sunny weather about 34C, and engine temp of my 3SCT usually around 116C - 122C.

The weather forecast on qualification day will be humid, colder maybe 28C, with possible rain.

What should I do, afm ?

Should I use 25% nitro ? C8TF glow plug ? Thank you for your racing tips.
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Old 05-22-2009, 12:22 PM   #4
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so what are the signs of an engine(12 size) that runs on the above percentages?? i already know how a 16% sounds and tunes but how about 20% and 25%, how can i tell if an engine is using higher percentage(16%) of nitro. thank you any respond will be helpful.
You can test the fuel for it's nitro content with Nitromax. I know that there
is a Nitromax 16% for testing 1/10 IC engine fuel.

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Old 05-22-2009, 12:56 PM   #5
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Tomorrow I have big race.

I usually use 20% nitro, C7TF glow plug, for normal sunny weather about 34C, and engine temp of my 3SCT usually around 116C - 122C.

The weather forecast on qualification day will be humid, colder maybe 28C, with possible rain.

What should I do, afm ?

Should I use 25% nitro ? C8TF glow plug ? Thank you for your racing tips.
I would not worry about changing Nitro % based on weather conditions. If anything I would maybe change the heat range of the plug. I only do this if the weather takes a big change from qualifing day to main day. On very humid days I might go to a slightly hotter plug. I normally use cold plugs; But with 16% fuel I use a Med heat plug just to give me a little better bottom end.


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Old 05-22-2009, 02:25 PM   #6
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so what are the signs of an engine(12 size) that runs on the above percentages?? i already know how a 16% sounds and tunes but how about 20% and 25%, how can i tell if an engine is using higher percentage(16%) of nitro. thank you any respond will be helpful.
In Europe, the touring gas is at 16%, mor than 16%, it not legal for race, more nitro, its more power, but its not legal for race in europe.
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Old 05-22-2009, 02:53 PM   #7
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Originally Posted by asw7576 View Post
Tomorrow I have big race.

I usually use 20% nitro, C7TF glow plug, for normal sunny weather about 34C, and engine temp of my 3SCT usually around 116C - 122C.

The weather forecast on qualification day will be humid, colder maybe 28C, with possible rain.

What should I do, afm ?

Should I use 25% nitro ? C8TF glow plug ? Thank you for your racing tips.
When humidity comes on the scene past 70%, it is best to move to a hot body glow plug. For example in your first case move to a C7TC, and I would not increase nitro. I think the C8TF is way to cold for a .12 engine and is best used with 30 to 40% nitro on a very hoy day.We should also state that without touching head shimming, and or cahnging nitro contents, a hotter plug will make the engine rev harder and a colder plug will make more torque.

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.
Inputs:
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.
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.


Hope this helps
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Old 05-23-2009, 03:34 AM   #8
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hmm very helpful information. so how differently does an engine sound from 16% or 20% to 25% or 30%. does the engine sound differently. afm you are very helpful.
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Old 05-23-2009, 07:23 AM   #9
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a hotter plug will make the engine rev harder and a colder plug will make more torque.

afm are you sure that this is not the opposite?
i think that the advance ignition give torque and the retard ignition rpm.
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Old 05-23-2009, 07:44 AM   #10
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hmm very helpful information. so how differently does an engine sound from 16% or 20% to 25% or 30%. does the engine sound differently. afm you are very helpful.
An engine sounds no different if you run 16,20,25,30% nitro thru it. It will sound different if you run 30% when you have it shimmed for 16%!!!!!
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Old 05-23-2009, 11:11 AM   #11
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ok thanks
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Old 05-23-2009, 05:22 PM   #12
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a hotter plug will make the engine rev harder and a colder plug will make more torque.

afm are you sure that this is not the opposite?
i think that the advance ignition give torque and the retard ignition rpm.

Experience dictates that just by lowering the head (more compression) you gain more power especially in lower rpm range, idle quality can suffer, but the engine runs cooler. Also, that a higher head (less compression) will increase top rpm speed on bigger tracks.
A decrease in head shims (an increase in compression ratio) will increase torque because as the compression ratio goes higher, the actual ignition timing occurs sooner. However there is a point of diminishing returns where detonation occurs or engine temps can soar, and if this happens a colder plug can help.
A colder plug will also increase torque, except in the instance of a colder plug; the ignition is slowed until a greater point of compression build occurs.
When you increase head shims (a decrease in compression), top end is enhanced as the ignition timing is retarded and occurs later. Generally a hotter plug is needed to advance the ignition cycle so that timing does not occur to late in the cycle, but at this point you end up over leaning the engine to get it to rev properly and the engine life will suffer dramatically.

A hotter plug causes ignition a little earlier in the combustion process and can have the same effect as “Advancing” the ignition timing and increase overall power output, especially at higher rpm.

There are limits, however, and installing too hot a plug can cause pre-ignition (detonation) and risks of damaging your engine.


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Old 05-23-2009, 06:31 PM   #13
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Originally Posted by afm View Post
Experience dictates that just by lowering the head (more compression) you gain more power especially in lower rpm range, idle quality can suffer, but the engine runs cooler. Also, that a higher head (less compression) will increase top rpm speed on bigger tracks.
A decrease in head shims (an increase in compression ratio) will increase torque because as the compression ratio goes higher, the actual ignition timing occurs sooner. However there is a point of diminishing returns where detonation occurs or engine temps can soar, and if this happens a colder plug can help.
A colder plug will also increase torque, except in the instance of a colder plug; the ignition is slowed until a greater point of compression build occurs.
When you increase head shims (a decrease in compression), top end is enhanced as the ignition timing is retarded and occurs later. Generally a hotter plug is needed to advance the ignition cycle so that timing does not occur to late in the cycle, but at this point you end up over leaning the engine to get it to rev properly and the engine life will suffer dramatically.

A hotter plug causes ignition a little earlier in the combustion process and can have the same effect as “Advancing” the ignition timing and increase overall power output, especially at higher rpm.

There are limits, however, and installing too hot a plug can cause pre-ignition (detonation) and risks of damaging your engine.


AFM
in the real world (bikes) i give advance and i have torque but lacks rpm.
i give retard and i have rpm but lacks torque.
i don't talk about huge difference in degrees.and of course there is not any detonation.

in the first occasion the ignition is created sooner and you have great performance in the low rpm.but when the rpm increase the dynamic compression is increased and in interrelation with the advanced ignition you have an engine that actually it 'tightens' in her own.

so still can't understand why here is the opposite.
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Old 05-23-2009, 07:22 PM   #14
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so...

1. 16% = more compression needed (less shims)
2. 25% = less compression needed (more shims)

which is better? or it's the same?
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Old 05-23-2009, 10:38 PM   #15
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so...

1. 16% = more compression needed (less shims)
2. 25% = less compression needed (more shims)

which is better? or it's the same?
You are right about compression changes with different nitro contents....which is better depends on what you are looking for

You don’t get fas much RPM’s with 25% nitro as you would with 16%.
With 25% you naturally have to richen the engine, it gives you more low end power due to the 25%...but just not all the power at top speed.
With 16% nitro you can lean it out for more top end power.
Why? because the flame speed of Nitro is much slower than that of Metanol, so by adding Nitro the mixture slows the flame speed. This should not be a problem until you hit very high rpm’s. There's a moment where the engine cannot pickup more rpm’s because it needs to burn the mixture at much higher speed in the combustion chamber. 25% also burns at a lower temp so it will give you advanced timing and therefore more low end power.
With lesser nitro, you may need to lean it a little more and your fuel mileage will be a little better, temps will vary and combustion chamber and carb setup need to be revised, but... more nitro doesn't necessarily mean more power, but yes more fuel consumption and less runtime for the same CC’s.
Higher nitro content does not cool the engine, in fact it creates more heat. Basically, more nitro = more oxidizer to the methanol which in turn creates higher combustion pressures which create more heat.

AFM
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