Back in North Carolina the gas pumps usually carry 87, 89, and 93 octane gas. As I've traveled out west I've noticed that the octane ratings are much lower. I've been lucky to find 91 octane, and usually the high octane stuff is only 89. Yesterday I went to a station that carried 83, 85, and 87. The "high-octane" was only 87! They are using the same calculation method, too, the R+M/2 method. What's the deal with the low octanes out here? I haven't noticed any pinging, but it just seems weird that the octane ratings would be so much lower.

 

maybe has to do with elevation?

 

Now that is a good point!

 

Bingo. In higher elevations you don't need the higher octane...the problem comes when you get down to lower elevations with the lower octane.

 

scientifically though, there has to be something to explain it...such as the combustion pressure generated using lower octane is the same at higher elevations. Or does it have to do with the 'ability' to induce combustion using a lower octane? I don't feel like googling, figured there was a engine guru around here with insight and knowledge of the principles in question.

 

This was discussed recently in the S type section. High altitude = lower ambient air pressure= lower cylinder pressure= lower requirement for octane. Result is lowered engine output too. Such is life.

 

Then why the heck do they charge me just as much? I've been paying $3+ per gallon for premium, and the "premium" is sometimes just 89 octane.

 

... because they can?

 

Can you spell Taxes?

 

Only 6 cents difference in gasoline taxes between S.Car, AZ, CO, UT, NM, OK, and TX.