Higher Octane Fuel (91+) and MPG in CS Mode?

[2BeLivingGreen]

I know as VOLT owners we rarely fill up the vehicle so data on this is likely rare or nonexistent. However I was just curious if using ultra high octane gasoline like 93 might show an increase in mileage when using the gas generator? Has anyone tried such a test? I am not talking about dropping down in octane but going higher from 91 to?.

Thanks for any info/data.

[DCFusor]

I've tried 87 and 93. On 93 I got high 30's, like 37+. On 87, only tried once, not pure (some super still in there) and it dropped to about 33, no pinging, guess is that they had a ping detector and retard the spark for that case. Seemed not worth it, so I didn't try more last winter when I was using gasoline.

[silvercorvette]

I always put in the grade recommended by the manufacturer. I haven't seen any 91 on the east coast but when I owned a house in TX and spent winter in TX and summers in NY they did have some stations with 91 which I used occasionally but for the most part the difference in price wasn't that much so if I had a choice I would buy 93 over 91.

Since the Volt does not use much gas I spend a few pennies more and only buy 93 I make it a point to buy top tier 93 even if it is more expensive than regular 93. I am also starting something new and after almost 50 years of driving keeping the tank full fro now on i will only put in $5 or less at a time. this way it will stay fresh, the last fill up way in early March. The only time I will fill the tank again will be if I am about to take a trip a few hundred miles long.

[Neromanceres]

People have this impression that higher Octane means better gas and this is simply not true.

Higher Octane just means the gas has a higher resistance to pre-ignition and means nothing to the effect of quality (In fact higher Octane gas can sometimes be worse quality wise). The Volts range extender was optimized for 91 Octane gasoline and this is where it will work best. 93 Octane should prove no benefit. 87 Octane will work but the engine will have to retard the engine timing and you will take an efficiency hit.

In short. Use the gas the car was designed to run on. If it was designed to run on 91 than use 91 if it was designed to use 87 than use 87 Octane.

[cnicholson]

I agree that 93 should ordinarily not proved a benefit, but it might-- and it certainly won't hurt. For most cars, the compression ratio is low and the engine rarely operate near full load. These are the circumstances where octane matters most. The car's timing and fuel/air mappings are pre tuned to a factory-set optimum. If the knock-sensor goes off too much, the engine will shift to a "safer" and less efficient mode. I don't know how sophisticated the Volt is in this regard, but let's assume _very_ sophisticated. Is your particular brand/condition of 91 still yields knocks, 93 may help. It is possible that 93 would help everyone-- it just depends on how aggressive the base tune is and whether 91 is causing the engine to shift to a less aggressive mode. I think you could see this with an OBD reader-- you wouldn't be able to hear/feel it.

For high performance cars, often 93 will yield more power, even though 91 is the manufacturer's spec and the car runs fine on it. I have a highly tuned street car where the mapping has been changed to be optimized at 100 octane, but runs safely down to 93 (which is still a bit of a challenge in CA when we can only get 91 at the pump....).

[TheProgrammerGuy]

Here is my two cents worth about premium. I have a 1976 Chevy Vega that I bought new. I have always put the highest octane gas in that I could find, at first because I didn't know any better (I thought it must be better because it's higher octane ), and now just because I always have. The car still runs great with no engine work done since I bought it. My point is that I don't think it will hurt anything.

[2BeLivingGreen]

I posted the original question based on one of the Audi forums where owners complaining of poor mileage were being told by other owners to use higher octane for better mileage.

[silvercorvette]

I posted the original question based on one of the Audi forums where owners complaining of poor mileage were being told by other owners to use higher octane for better mileage.

Which is quite possible, the engine will adjust itself to run on lower grade gas and that may be the reason for lower MPG.