[Cdnwolf]

Effects of Air Pressure

Altitude decreases an engine’s octane requirements because of the change in air pressure. The higher elevations have a lower level of air pressure, which means an engine needs less octane to properly fire due to the lower ambient pressure. In certain states, such as Colorado where the altitude is generally above 5,000 feet in the mountain regions, 85 octane gasoline is sold, while in lower elevations 87 octane is the lowest sold.


When an engine requires lower levels of octane to “fire,” the overall efficiency of the engine is also lowered, which means the engine works harder to achieve the same results. However, less fuel burns, which means the overall fuel-per-mile efficiency is increased because the engine is working at a reduced compression rate. In short, you can get higher miles-per-gallon at higher elevations, but the power of the engine is also somewhat reduced.

http://www.ehow.com/about_6744997_ef...#ixzz2WlabP63P


Methanol and ethanol have an octane rating of about 98-99.