Gasoline means a mixture of isooctane, which is conventionally assumed to be 100 units, as it is practically not volatile at elevated pressure and normal heptane is taken as 0 units. It is practically not resistant to detonation at higher pressures. The octane number of gasoline 92 so that it detonates as a mixture of 92% isooctane and 8% normal heptane. Usually after primary distillation of oil octane number less than 70. To improve the quality of gasoline antiknock additives are used. Currently, the most used ether methyl-tert-butyl (MTBE). It has huge advantages over the previously used lead antiknock additives, which adversely affect the environment and human health. There are gasolines with an octane number greater than 100 units. They use a different volume with isooctane additives.
The combustion rate of gasoline depends on the octane number. Gasoline with a high octane rating burns more durable and smoothly without causing shock loads on the pistons in the combustion chamber. The motor will work clearly and evenly. It is because of this modern auto industry produces cars with engines that run on high-octane gasoline.

Low octane gasoline ignites at a time when there are not closed intake valve, and the cylinder is at the top. Naturally, the engine will not operate at full capacity plus the wear and tear of valves, saddles for them, extra carbon etc.
To increase the octane number of gasoline are special additives that are added to the fuel. They can be purchased at any automotive store or automotive gas station.
there are times when you need to lower the octane number of gasoline. Sorry, not in the same technical literature does not describe a specific method how to produce, how to turn expensive high-octane gasoline in a cheap fuel with a low octane rating is not economical. Octane can lower it,
1. The addition to gasoline of tar and sulfur compounds.
2. Add in high-octane gasoline fuel lower-level lower octane first.
3. A long standing gasoline. Over time the gasoline left in any capacity, lowers octane. This decrease occurs from 0.2 to 0.5 units per day.