RC Car Basics Part 1: Fuel Basics
There are a lot of mis-conceptions out there about RC fuels. On the market today there are many brands of fuel, but most differ with respect to their lubricants used. The oils used in the RC fuels are essential to keep all the engine’s moving parts working freely and to remove heat from major moving components. Lubricants used in nitro RC fuel are either purely synthetic or castor oil, or a blend of synthetic oil and castor oil. As everyone knows, a coating of oil prevents metal parts from rubbing against one another, and avoids extensive heat build-up and excessive or premature wear on tightly tolerated parts(piston and sleeve). The type, quantity and blend of lubricants in a fuel, are the most closely guarded secrets in the business and are usually not disclosed, not even to the distributors. A few manufacturers are now disclosing lubricant content (Wildcat, HPI) as in oil % but not in specifics of how much of each type or even types of oil. Most manufacturers will just say 12% oil not 6% castor and 6% synthetic. It seems that more people today will buy fuels which give oil content so that they know there engines are getting the required oil to preserve their investments. Some other major companies like Traxxas and Blue Thunder still hold it as their secret. Certain adopted Industry Standards such as how the fuel is blended by Volume give the fuel a more exact mixture, where as a few fuel manufactures still like to blend fuel by weights of ingredients.
Castor oil promotes cooling while Synthetic oil protects engine components from wear. Some fuels contain only castor oil and most contain either both types of oil or only synthetic oils. Big block motors in my experience have a tendency to favor the castor oil fuels. This helps them run a little cooler and crisper, where as smaller engines, which rev a little higher, like the synthetic blended fuels.
The flash point is the temperature at which a lubricant will burn during combustion in the motor. Lubricants with a high flash point tend not to burn at all leaving the engine loaded in oil. As we all know this will keep the engine well lubed up, but may affect your performance. Lubes with a lower flash point tend to burn with the fuel, and this leaves a cleaner combustion chamber for the next cycle. You sometimes here people refer to the fact that your motor seems to have a 4-stroke sound, when you hear this, this is your motor running slightly clogged up (this also happens when running fuels with high oil content, in which the oil isn’t burning away).
WHICH PERCENTAGE OF NITRO SHOULD YOU RUN?
Everyone you seem to ask has a different opinion of what type of fuel to use. No fuel is ideal for every application or is it a fact that a higher percentage of nitro results in better all round performance. The correct percentage of nitro in a fuel and its effects on engine performance are rather complex issues due to the many variables as in climate, humidity and glowplugs used. To understand how nitro content affects engine performance, it helps to have a little basic understanding of nitro.
- Nitromethane is a monopropellant which means it can burn in the absence of air.
- Nitro Methane contains nitrogen and oxygen, which provides more “fuel” for the combustion process
- The oxygen contained in nitromethane is released during the combustion process allowing richer needle settings that pack more fuel in the combustion chamber.
- More fuel plus more air potentially equals more horsepower when engines are designed to run on fuels containing nitromethane or the amount of nitromethane that you run.
There are a great deal more technical aspects to Nitro Methane, but this explains why you can produce more power with it.
Now running more nitro does not always mean more horsepower, the engine has to be designed to run the amount of nitromethane you intend to use. Running 30% nitro fuel in an engine designed for low to no nitromethane content, will not yield anything but poor, hot running engine characteristics. Using 0% nitro fuel in an engine designed for 20% or higher nitro will yield equally poor running engine characteristics.
RC cars and trucks with engine sizes .12–>.18 usually use 10%-20% nitro content fuel with 8%-16% oil content. It is hard for one person to tell you which fuel to use for your particular vehicle due the varying conditions of your surrounding area. If you wish to find out what really works, go down to your local track to see what everyone uses, that’s the easiest way. RC cars and trucks with engines from .21–>.27 typically use more nitro content. The common range is from 20%-40% and around 8%-18% oil content. Fuels have different oils, and at different altitudes their flash points are different, so some people say a particular fuel is good, but for someone else it is not. It is mostly trial and error for which fuel will run best for your liking.
Nitro RC fuel is a Methanol-based fuel. As people learn in Chemistry, Alcohol has a very Rapid evaporation rate. Which given time outside in warm conditions accelerates that evaporation. If you look at your fuel bottle on any given day, you will see tons of tiny droplets on the inside of the bottle. These tiny droplets are the alcohol (methanol) that is evaporating out of the fuel. Most people believe this to be accumulated moisture from the outside world but its not. If you to some of the serious racers out there, they say it is a good idea to keep your fuel in a cooler. This helps keep it cool on a long day of racing, and also keeps it out of the sun and humidity.
Since Methanol evaporates so quickly, it is very important you keep your caps on your fuel bottles, and also on your quick filler bottles. Even with the bottle capped, severe changes in climate can accelerate evaporation inside the bottles. If you have to store fuel, even for a very short time, keep it out of the trunk of your car, and off the basement floor. You want to keep you fuel in an area where the climate remains relatively constant. Never store fuel near heat vents or in direct sun light. Store it in a dark, cool, dry place. When you store your fuel in the basement, or your garage, use plywood as an insulator between the bottle and the floor, because plywood is fairly resistant to letting moisture through. If you don’t have any plywood, use a thick carpet or even put it up on a shelf.
Most people believe that keeping fuel in metal containers is better than plastic ones, but they both have their flaws. Metal containers are usually roll crimped, not welded or soldered shut. With these crimps, they are not 100% sealed, and after time air starts seeping into the cracks. Plastic seems to seal better than the metal containers making them the ideal thing to store fuel in for longer periods of time.
If you are careful, and avoid conditions stated above, you’ll be able to safely store fuel and use it up to two years later.
Which if you are into RC will never happen!!