Using 91 octane to boost MPG?

[theaveng]

While researching the Chevy Volt I saw that it's 10.5:1 engine requires 91 octane. The GM engineers explain that the higher compression provides 5-10% better fuel economy. The insight has a 10.8:1 engine. Perhaps it too could see 5-10% better economy like the Volt engine?

I've tried using 91 octane fuel but can't say I've seen any difference in MPG. It does seem to have better mountain-climbing ability though.

[AbCaRed00]

Top Tier brand 87 aki for me. No diff with higher octane 92 aki. This one is well worn topic.

[diamondlarry]

The only reason I see it making a difference would be if the 91 octane was alcohol free/E0.

[spets]

Our engines are not designed for a higher octane, so you won't see any real benefit from switching unless it is non-ethanol or you're already detonating at 87 octane.

[Cobb]

Interesting, we also have a 10.8 to 1 compression. Many have found that BP gives the better fuel economy and mid grade helps a little with both, but its not worth the extra expense.

Ive seen 91 as well as 93 at some stations. Have you tried 93? I see rom use of an octane booster under aggressive driving its more behaved in regards to reving and cvt adjustments, but not for mpg.


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[Eli]

Combustion chamber design(among other things) factors much more than compression ratio when it comes to the octane of fuel required.

Honda designed the Insight's 10.8:1 compression ratio engine to run on 87 octane.. because they have the skills to do that.

Apprently GM does not.

[RedJellyBean]

Nothing but the worst for my car! I discern no difference between Kentucky RFG gasoline and Ohio E10, they both give about the same MPGs. One time I did get to fill up at an ethanol free station in Oklahoma but even then I didn't notice much of a difference. Since my car doesn't care, I don't care either.

[theaveng]

Originally Posted by spets

Our engines are not designed for a higher octane

Okay. The Volt's engine has a lower compression than our engine. Why do you think they require 91 then?

I notice my tank runs out of fuel faster (fewer total miles) with E10 because it has less energy.

[spets]

Maybe GM decided to use advanced timing for greater fuel efficiency and that required 91. Or different combustion chamber design like Eli said. I don't know the particulars of the Volt engine so all I can do is speculate.

[theaveng]

The Volt engine is also used in the 42mpg CruzeEco turbo, but the cruze only requires standard 87. So maybe it truly is just "advanced timing" rather than high compression. (Does the insight use advanced timing when fed 91 octane?) If that's true you could probably run standard gasoline in your Volt.