Fuel Mixture Workshop
by Eric Perez


Welcome to the Nitro Fuel Workshop!

Here we will teach you how to make your own custom blends of Nitro-Methane fuel for your 2-cycle radio control car, truck, buggy, airplane, helicopter, boat, anything nitro powered!

The Basics
Experiencing the frustrating problems of engine overheating and either being permanently damaged or flaming out is something that many people who run nitro engines will experience at one time or another.  Understanding the reasons for these problems is the first step in solving them.

The relationship of fuel, it's lubricant additives and your engine is a delicate one that is often either overlooked or avoided due to its seemingly daunting complexity.  This general misconception about its complexity or its lack of importance is critical to overcome in order to successfully bridge the gap between the casual back-yard basher and the serious hard-core nitro racer.

This is not to say that the casual user won't benefit from this knowledge, and in fact, many such users will find the concept of mixing their own fuels and gaining an understanding of how it impacts their engines a fascinating venture.

Fuel & Lubricant Primer

Nitro Engine Basics
Nitro engines run on a highly combustible mixture of methanol, nitro methane (CH3NO2) and castor or synthetic oil.  Rather than using spark plugs, such as in typical 4-cycle engines, these engines use a method of combustion similar to diesel engines (granted diesels are generally 4-stroke).

Using electrical current and a glow plug, a hot spot is created in the combustion chamber.  This, in addition to the compression of the moving piston, creates the combustion cycle.  Within seconds, the combustion chamber and glow plug become extremely hot and maintain subsequent combustion without the need for the electrical "jump start".   This is what is often referred to as "dieseling".  The only thing that breaks this cycle is either lack of oxygen or fuel (or an un-timely death of the engine).

Nitro-Methane Content
Fuels are rated by their nitro-methane content, typically 10-40%.  The higher the nitro-methane, the more power to the engine.  Typically in 1/10 scale cars (with .12 engines), 10-20% is plenty sufficient.  More than that on these smaller scale cars will go wasted, since the engines to not efficiently convert use the extra-potent fuel and the hookup (traction) is usually marginal, at best.  They heavier 1/8 scale and larger cars can see significant increases in usable power by using these higher (30% and higher) nitro-methane ratings.  Often engine temperatures are actually improved (lower) with higher nitro-methane contents because a richer setting can be achieved without adversely affecting throttle response.  This is an important consideration when deciding on your blend of fuel.

In-Fuel Lubricants
These engines do not use any auxiliary method of lubrication.   Instead, they use the same method of lubrication found in most other 2-cycle engines.  Because of the physics of 2-cycle engines, the fuel passes both sides of the piston, including the crankcase.  This allows a convenient method of lubrication.  By actually combining the lubricants with the fuel, you can continually coat all the moving parts of the engine as the fuel makes its way to the combustion chamber.   Whatever lubricants are not absorbed by the metal they come in contact with are either burned in the combustion chamber or are discharged through the exhaust port.   This is why you will often see these broken down oils seeping from the mufflers or tuned pipes.   It is just the normal process of cycling through the lubricants. 

Most nitro-engine manufacturers recommend using a special "break-in" fuel which contain a higher percentage of lubricants for the first few dozen tanks or so.  This is to insure that the engine has plenty of lubrication in order to properly break in and maintain a good seal in the combustion chamber. 

This is also why we encourage users to tune their engines slightly rich (see Engine Tuning & Maintenance) so that there is a sufficient supply of these lubricants to  the engine.  Although running your engine lean may increase performance (temporarily anyways), it will be short lived if the engine doesn't have enough lubricant to maintain proper engine temperatures.

Oil content is one of the largest factors in engine temperature and generally speaking, the higher the oil percentage, the lower the engine temperature.  Finding that perfect blend is a matter of trial and error, because the more oil you put in your fuel, the less percentage there is of other ingredients. 

The Disclaimer

This one is an important one, because we want you to understand that any modifications you make to the fuel that runs your engine can have serious side affects.  If you are not confident in mixing your own fuels (for whatever reason, whether it be personal and property safety or engine longevity issues) please do not attempt to mix your own fuels.  Nitro-Methane fuels are extremely flammable and caustic.  If you are under 16 years old, you should only do so with parental supervision.  I'm not kidding about this one, fuel is not a toy!  Respect it and you'll get along fine, abuse it and you'll eventually pay the price.  We at NitroRC.com cannot make specific recommendations for fuel blends nor do we or any of the authors take any responsibility for any damage to you or your equipment.  This information is to be accepted as a "As-Is".   For more information about our disclaimer, click here.

To Summarize

A few things to keep in mind when making your custom fuel recipe:

  • Most engines are designed to run on 14-20% oil content.  This variation is dependant on engine and application, but most sport users should not go below 16% because of increased engine wear and temperature which will shorten the life of the engine.  Above all, your oil content should be sufficient to maintain a 200-215 degree temperature
  • Colder climates can handle lower nitro percentages better than higher nitro contents.
  • Higher nitro-methane percentages yield more power
  • Adding any component to fuel will automatically decrease the percentage of other components already in fuel.  If you have 10 ounces of Substance A and 10 ounces of Substance B in a glass, for example, you have a 50/50 mixture.  Let's say you then go and add 10 more ounces of Substance B.  You've increased you percentage of Substance B, right?  Well, yes, but you've also decreased your percentage of Substance A.  You still only have 10 ounces of Substance A, but you have a total of 30 ounces of mixture, and only 1/3 of it is now Substance A.  You've decreased Substance A's percentage from 50% to 33% and increased Substance B's from 50% to 66%.  Sound complicated?  Well, not really, that's why we're here to calculate this for you.

Getting Started
To begin mixing your own fuel, begin by choosing whether to blend your own fuel with both nitro-methane and caster/synthetic oil, or just the oil by itself.  Adding oil to your fuel will slightly decrease your nitro-methane percentage content.  If you want to retain the same nitro percentage after adding oil, you will have to purchase at your local race fuel supplier.  

If you can live with a percentage or two drop on the nitro content, then you can just add oil and not worry about having to purchase other fuel components to reach your "perfect" fuel blend.  In this case, you can just click on "Add Oil Only" below and the drop in percentage for nitro content will be calculated for you.   

On the other hand, if you're going to the trouble of purchasing nitro methane (or just happen to have some lying around), then you might as well go for broke and generate a recipe for both oil and nitro by clicking on the "Add Nitro & Oil" button below.




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This page last modified: 07/26/11