When you walk into today's hobby shops, you have many choices of manufactures of fuel. Within each manufactures line of fuel they have different mixtures regarding the nitro percentage of the fuel. The nitro percentage can make a very large difference in the set-up and tuning of your engine.

First, check the instructions that came with your engine. The instructions will usually include a recommendation for the proper nitro % to be used with the engine. Sometimes the engines will even come with an additional head shim in case you will be using a higher nitro % fuel.

Most on-road and off-road engines are set-up to use 25% nitro fuel. There are cases where the .12 & .15 engines are set-up for 16% nitro as this is the legal limit in Europe (where most of the engines are produced). When the nitro % isn't regulated ( U.S. races) it can be used to a driver's advantage to adjust the nitro % of their fuel. Here are a few tips for different situations to adjust the nitro % and engine set-up to match your racing needs.

In 1/8 scale racing with .21 engines it usually is a balance of power and fuel mileage. Running 30% nitro will give you more power but you in turn sacrifice fuel mileage. When you switch from 25% to 30% you need to raise the head clearance of your engine to compensate for the larger explosion in the combustion chamber. If you don't, your chances of breaking a glow plug will increase as well as the chance of blistering the top of the piston and combustion chamber. Now, while more nitro actually lowers the flash point of the fuel it still tends to build more heat into the engine, as the explosions are more volatile. This means you will have to richen your engine to keep your operating temperatures the same – this is where the decrease in fuel mileage comes from. I have run many races using less than 25% nitro in my 1/8 car. It gives great fuel mileage as well as a very consistent running engine that allows you to tune it to the limit.

In 1/10 racing fuel mileage isn't as much of a problem so it is possible for drivers to push the limit with the nitro %. This can yield loads of power but keep in mind you have to set your head clearance very carefully to get the most out of it. Also, as you add more nitro % the window of error becomes much smaller. A lot of times you see guys who use higher nitro content have extremely fast cars out on the track, especially in qualifying. The problem comes in the final, as the heat builds in the car, you will see that driver have a very hard time keeping the tune on the engine. Flame outs during pit stops and at the end of long straights is one of the tell tale signs, provided the engine is in good condition.

Nitro content can help you and hurt you in several ways. It's best to keep a close eye on your glow plug condition after each run as well as the condition of the piston and head button. These will let you know if you have pushed the limit too much with your tuning and set-up. Be patient and have fun!!

Good Luck!!
Josh Cyrul
CEFX