octane rating and engine performance

I tried the 85 when I was in CO. no thanks! it felt like the X had 50 less HP. I run 89 no matter what. it makes a difference, even at elevation!

Coolmom is exactly correct. You don't need the higher octane in higher elevations because the elevation is limiting the amount of air that gets in your engine. (unless you are supercharged)

If OEM says use the cheap stuff at sea level then use the cheap stuff a altitude no matter what the number is.

One caveat. If it is really hot and your towing very hard at WOT for long periods "I" would jump the octane to mid grade or even premium.

Yes two points will make a difference depending on the vehicle and the conditions.

I was trying to find the study that was done some time last year where they tested multiple dual fuel vehicles. Some recommended 87 but were able to increases performance with higher octane and some recommended 91 but were able to lower engine performance with lower octane. One of those vehicles was an F150 Ecoboost.

These vehicles were able to adjust their injection timing, valve timing, and ignition timing for different fuels depending on how much knock was detected by the wide band knock sensor. However, they can only adjust them so much and after a certain point they could not do anything to mitigate knock. In normal driving this was not an issue, but the research showed that under hard driving conditions with high load and high engine temps, the slight octane rating difference had a big effect on the engines ability to deter knock and performance.

If I find the research paper I will post it. I posted it here before in a discussion about the F150 ecoboost.

sgip2000 wrote:
Look carefully at the pumps too. Some states also have non-ethanol. That affects the octane rating.

That is an unnecessarily confusing statement.

The octane stated on the pump IS what it IS.
87 is 87, regardless of what the ingredients are.

drsteve wrote:
What coolmom said. Your truck will run just fine on the 85 octane.

BUT.....don't run the tank empty and then fill it up with 85 and then go back down to sea level to actually use the 85 fuel. THAT might not work out too good.

If you will be going back down to lower altitudes before most of the gas is used up, I suggest that you fill with 87.

Look carefully at the pumps too. Some states also have non-ethanol. That affects the octane rating.

What coolmom said. Your truck will run just fine on the 85 octane.

patperry2766 wrote:
In Texas, the minimum octane rating is 87. On a recent trip to Glacier, I noticed a lot of the fuel in states like CO, WY and MT, the octane was 85, and you had to buy the mid-grade to get 87 and above.

Will 2 octane point decrease really make much of a performance difference?

No.

The lower octane rating is available at higher elevations. At that point, the air density becomes the limiting factor in engine performance. Extra "octane" is a waste in engines that don't require it. (Just like anything above 87 is a waste in engines not designed for it.)