Octane lower at higher elevations

[Skipg]

I've noticed at higher elevations the octane levels are lower than what I am used to.I always use regular 87 octane at higher elevations my choice here is 86 or 88 octane. What should I use. I have a 2006 Ford V10. Thanks
Skip G

[DanTheRVMan]

wolfe10 wrote:
At higher elevations, effective compression ratio is reduced (less molecules). So, lower octane fuel will work fine.

The problem-- a big problem is to fill with that low octane fuel and then go down in elevation, particularly if there are still steep grades at that lower elevation. If that is where you are headed, better to pay the extra for the higher octane fuel.

Yes

At elevation there is lower air pressure and lower partial pressure of oxygen (less oxygen)

so you can use lower octane

[donsuefuggrwe]

Spending summers in Gunnison (7705 feet elevation) and Crested Butte (9000 feet) Colorado for many years now. Always have used 85 octane fuel here and milage would increase from 25 MPG to 30 MPG in the 2000 Suzuki and from 22 mpg to 27 mpg in the Honda CRV. No difference in performance here or off the hill when still using the 85 octane. Also on dirt and 4 wheel drive roads up to 12000 feet. Use the 85 stuff.

[JimM68]

kinda simple. All else equal, a higher elevation does not require as high an octane as a lower elevation, excalty as Brett said.

Octane is only resistance to knock, it is basically a function of dynamic compression ratio. Less air, less compression, less octane required.

A higher octane fuel than the conditions require will not yield more power.
Modern engines can adjust for a "too low" octane by limiting the ignition timing.

[J-Rooster]

Skipg wrote:
I've noticed at higher elevations the octane levels are lower than what I am used to.I always use regular 87 octane at higher elevations my choice here is 86 or 88 octane. What should I use. I have a 2006 Ford V10. Thanks
Skip G

Skip, I live in Washington State, when I would ride my Harley Davidson to Sturgis, South Dakota for bike week. I noticed the octane would lower when I was headed East on I-90 after leaving Idaho! I had friends who I rode with that would adjust there ignition module (under there seat) to deal with the lack of octane! Very interesting question!

[BTPO1]

I go for the higher octane, it is only a few cents higher. JMO

[wolfe10]

At higher elevations, effective compression ratio is reduced (less molecules). So, lower octane fuel will work fine.

The problem-- a big problem is to fill with that low octane fuel and then go down in elevation, particularly if there are still steep grades at that lower elevation. If that is where you are headed, better to pay the extra for the higher octane fuel.

[Golden_HVAC]

With lower octane, the engine is a little more prone to knocking. The engine has a anti-knock sensor, and will make the fuel system run rich and retard the timing to keep it running knock free. Both of those will lessen the fuel mileage.

So my best advice for good fuel mileage is higher octane.

At a higher altitude, you can use reduced octane fuel, it will not be as likely to knock, however the engine will retard power and enrichen the fuel mixture if you use it.

Fred.

[rgatijnet1]

86 or in some places 85 octane will work fine.