93 octane above 5000 feet?

February 17, 2005, 03:09:44 AM

I was curious why I couldnt get 93 octane here, and everyone always talks about it. So I did a search and found this

Since I live at 5000 feet, I wondered why I could only get 91 Octane. According to my research, the octane number is a rating of how much octane or equivalent additives have been added to the gasoline to prevent knocking. Knocking noise comes from the cylinders detonating without spark. Detonation of fuel will occur with spark or under pressure. This is much like a diesel engine. The lower the octane number the lower the pressure required to detonate and the slower the fuel burn rate. Higher octane fuel requires more pressure to detonate and burns faster. Therefore, one of the advantages of using higher octane fuel is that it runs cleaner because of the fuel burn rate. The reason you can only get 91 octane at higher altitudes is because 91 has the equivalent octane effect as 93 due to the partial pressure of oxygen and air in the cylinders. Unless your car is tuned for higher octane and takes advantage of the fuel burn rate with advanced timing, it is probably not doing anything when you fill up with higher octane gas.

I am just curious if this is true?