This in an everlasting discussion subject in R/C circles. "Nitro, what it does and does not do."

Some of the theories are tales of legend which keep alive some amazing myths, many of which I have read on this website.

Basically, Nitro is a power enhancer. By its chemical composition, it increases the amount of oxygen available in the fuel for combustion. Use of small amounts will help the engine run smoother, especially at idle.

Nitro WILL NOT increase RPM. But in the combustion process, it helps produce more energy, so the engine will produce more TORQUE, allowing the use of a bigger propellor, or better operation under high load.

It's use is common in competiton R/C aerobatics (Pattern),where competitors use high nitro content fuel, so they get better performance increase in vertical climb.
5% more Nitro content, can be the difference between running a 12 x 11 prop or a 12 x 12 prop at 10,000 rpm.

The downside of all this is that the more nitro in the fuel, the more heat is produced by the engine in the combustion process, so cooling also becomes and issue.

It also contributes to rusting of the engine internals, caused by the acidic by-products of the combustion process. This is especially so in 4 strokes, where a lot of "gunk" residue is left in the crankcase (for the engine bearings to bathe in) when the engine is not running.

Just how much more effective higher nitro will be for your engine will also be determined by its compression ratio. High compression 2 stroke engines from Europe, where nitro is expensive (MVVS etc ) don't need much at all. They are designed to run on FAI fuel, but will tolerate up to 5% o.k. Anything above that and your wasting $$$$.

2 stroke Engines produced in Asia and North America generally have lower compression ratio's and are usually designed to run between 5 and 15 % nitro content. Some engines, such as Dubb Jetts, may even need more.

There are some exceptions to this however. For example, Super Tigre, which although now made in Asia, is a European design and needs little if any nitro (0-5 %) and MDS which although originating in Russia, follows the Asian design practice (needs 10 % and higher.)

Larger, lower revving 4 strokes (with the exception of Laser's) are designed for between 10 - 20 %.

The best recommendation is: read your engine manufacturer's recommendations and go with what they say. After all, no one will know more about an OS engine, than OS!! Even on this website.