Rocky Mountain High—(octane)





All of my life, I have been used to the high altitude here in Colorado and never really gave it much thought. In fact, the altitude has been pretty well taken for granted by us “locals.”


Since the article “Attitudes About Altitude” and other articles about high altitude tuning, etc. were written for coming to the Grand National this month, things have changed.


It seems that our “high” altitude is a big fearsome mystery for our lowland friends. At least that is the impression I am getting from all the calls and letters coming in regarding life and visiting at this altitude.


I even received a letter from Mr. Bentwrench of The Self-Starter fame. He presented a question that has had me curious for years. The basic question is, why do they sell higher-octane fuels at sea level than you can buy at locations considered to be “high altitude?” After driving to Santa Clara, Calif., a couple of years ago for a Grand National, it was obvious that there was a three-point spread in octane rating in all available grades of fuel. This wasn’t the first time I had noticed this oddity, so, nothing would do but to conduct further research.


I found that there are as many answers and/or theories as there are people asked. One consistent answer that came from so called “experts” is that at 6,000 feet above sea level, you get the same performance from 90 octane as you would get with 93 or higher octane. Also, it seems that the higher the octane, the higher the cost to produce. According to some, this becomes a profit motive for the oil companies.


I do know from personal experience over the years that higher-octane fuels will let your car start better in cold winter weather. On the other hand, using lower-octane fuel reduces vapor locking in the warmer summer months, especially at higher altitudes. Remember that we in Denver start out at 5,280 feet above sea level and drive above 14,000 feet at times.


The most logical answer that was found to this question is that due to the thinner air with less oxygen, the fuel mixture can only burn so fast; therefore, there is a direct ratio between air density and fuel volatility. To exaggerate a bit to prove this point, you all know that all gasoline regardless of octane rating will not burn in a vacuum. All pilots know that the higher the altitude, the leaner the fuel mixture you use for cruising. Of course, most airplanes fly higher that you will ever drive your car.


It all boils down to the fact that the big worries that have been expressed so far don’t mean a hill of beans as far as enjoying yourself at this altitude (non-Bronco fans excluded). All of us who live here enjoy our atmosphere, rather than worry about it.


It also boils down to whichever theory with which you want to concur. As for me, well, the one about higher profits for the oil companies is very high on my list, so, I guess I will just enjoy my own “Rocky Mountain High” and not worry about octane rating, or anything else I can’t control.


See ya at the Grand National.