[Jackpine]

The Ford Owner's Manual says you shouldn't use gas rated lower than 87 octane, but I have, when that is the "regular grade" and have experienced no problems. The regular grade in Colorado Springs and similar higher altitude locations is 85 octane.

If you operate the truck at high altitude or in an area of very high temperatures, the air is less dense. This has the effect of reducing the actual compression in the engine because even though the "ratio" is the same (9.85:1 as an example), the "1" part is less than atmospheric pressure at sea level (14.7 psi). So, multiplying that lower pressure by 9.85 gives a lower compressed value and less tendency for the air/fuel mixture to detonate (ping). As a result, you don't really need the increased anti-knock properties of the higher octane.

You don't need a new tune if you burn 86 octane where you drive. You see 86 octane gas there because of the elevation (3740 ft) and the generally warm temperatures.

Switching the gearing to 4.56 will not merit a new tune either. But, you will want to change the Gear Ratio to that value in your Custom Options when you tune your truck to make the speedometer and odometer read correctly and to have the truck shift at the appropriate points.

- Jack