What gas octane???

Targa wrote:

jimbow2 wrote:
Users of the big gassers: Dodge 6.4, GM 6.0, Ford 6.4....... Can the lower octane be used or do you need the higher octanes????? Colorado we have either 85, 87, or I think 91..

Word on the street is that due to our altitude in Colorado 85 octane is equivalent to 87.

Last year 80% of the gas sold in Colorado was 85 octane and only 9% was the mid grade 87. I've been driving here at altitude for almost 50 years with assorted vehicles and have never had any issues using the 85 octane. Now if Costco sold the 87 octane (only 85 and 91) I might be convinced to switch.

http://www.denverpost.com/2006/10/16/some-knock-states-lower-octane-levels/