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Discussion Starter #1
My commute each day is roughly 155 miles. With that said, I fill the tank on average about every 4 days. I decided to run a test on Mid Grade fuel, and see where the average MPG would go... After running 2 full tanks of Mid Grade, I've seen my average go from 42-43 on Premium, down to 37-39 MPG on Mid Grade..

I have to say I'm really surprised by this.


All the variables remained the same between the 2 types of fuel;
I drive 66-69 MPH
Use Hold for the 1st 3/4 of the trip, then switch to Battery for the last 40 miles
Same route each day
Running the ICE, I use "Fan Only" and just rely on engine heat


When I drove my LS430 on the same commute, I ran regular, simply because of the cost savings over Premium ($60 every three days VS $75 for Premium) and I really didn't notice much of a difference between the 2 fuels in regards to economy, simply because driving on the freeway wasn't calling for much of a demand on that V8. I would average 25-26 MPG per tank regardless of what fuel I ran.

So, I guess I'll continue to run Premium and see if there's a marked increase. Although with the colder temps approaching, I'll be using more than just ICE heat on the way home in the afternoon.


Fascinating car....
 

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So, roughly 10% less economy...but the stated difference in fuel cost is 25%. Might be a no-brainer for you?

Probably more data points with the Volt is in order.
 

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Discussion Starter #3
The cost between Premium and Mid Grade is only about 3.50 per tank, which comes out to a measly 18-20 dollars a month savings. I haven't ran regular in the Volt, and nor would I. I think with the continued demand on the ICE engine while driving in Hold Mode, it does benefit from the added octane of the Premium, and the extra cost is negligible.
 

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If you have Torque, or any other scan tool watch what your knock sensor and timing retard is doing when you run anything other than premium in it. It is literally screaming, begging, and doing anything it can to save the engine from destroying itself.

Anything other than Premium is not an option, no matter what anyone else says.
 

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Discussion Starter #5
If you have Torque, or any other scan tool watch what your knock sensor and timing retard is doing when you run anything other than premium in it. It is literally screaming, begging, and doing anything it can to save the engine from destroying itself.

Anything other than Premium is not an option, no matter what anyone else says.
I use the Torque program and read a minimal difference in timing while the engine is running on the freeway (light load)

At the low RPMs of freeway driving, the engine demand is such that the lighter load does not call for increased power output.

That being said, the occasional increase in RPM while the Volt is running the engine, probably warrants the higher octane fuel, for better efficiency.


I'll need to see documented proof where a lower octane fuel "destroyed" an engine.
 

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Sounds to me like the Gen 1 Volt shares the Gen 1 Cruze's dual octane map for ignition timing. The ECU "listens" for pinging and predetonation and falls back to a far less aggresive ignition timing map to protect the engine from damage. The 1.4 engine shared by the two cars is designed for 91 octane; running on a lower octane will cause the ECU to throw away power in order to protect engine. You might be able to run mid-grade in the winter but in the summer your Volt will struggle once out of battery.
 

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I use the Torque program and read a minimal difference in timing while the engine is running on the freeway (light load)

At the low RPMs of freeway driving, the engine demand is such that the lighter load does not call for increased power output.

That being said, the occasional increase in RPM while the Volt is running the engine, probably warrants the higher octane fuel, for better efficiency.


I'll need to see documented proof where a lower octane fuel "destroyed" an engine.
The engine runs at WOT most all the time, save for transitioning between warm up and full load. Engine speed is maintained by generator load and timing changes. The throttle plate remains wide open to reduce pumping losses.

The engine's 11.0:1 compression is what dictates the requirement for premium, more so than fuel longevity or efficiency. Lower octane fuel actually has slightly more BTU's but has a higher tendency of auto ignition.

And lastly, I'm not documenting anything for you. Without that knock sensor the engine would quickly rattle itself to death. Your car, do what you will with it. But you do have the tools to know what it's doing, so listen to what it tells you. I'm not one for relying on a solitary sensor to save my engine from arrogance or ignorance.
 

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Discussion Starter #8
The engine runs at WOT most all the time, save for transitioning between warm up and full load. Engine speed is maintained by generator load and timing changes. The throttle plate remains wide open to reduce pumping losses
Not my experience thus far. the engine will run up to 2800 +- RPMs occasionally while driving on the freeway, but it stays in the 1300-1500 rpm range most of the time I'm on the freeway.

My commute is 90% freeway, so I don't have a lot of data for city driving.
 

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Discussion Starter #9
And lastly, I'm not documenting anything for you. Without that knock sensor the engine would quickly rattle itself to death. Your car, do what you will with it. But you do have the tools to know what it's doing, so listen to what it tells you. I'm not one for relying on a solitary sensor to save my engine from arrogance or ignorance.
Never asked you to document anything my friend. Relax...

I simply stated that I would have to see documentation of an engine being damaged by low octane fuel. Thus far I have not seen that.

It's all good....
 

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We're good.

Engine rpm and throttle angle aren't the same in this car. it may be puttering along at 1500 rpm, but if you watch the throttle angle it's wide open. The controllers manage engine speed through resistance on motor/gen A and slight timing changes.

Here's a screen shot of some data logging I did with HP Tuners on lower octane. The box to the right is a histogram and the red is how many knock counts and how much timing was pulled in each cell.

Screenshot (23).jpg
 

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Discussion Starter #11
Actually, that's pretty good real world data in that screen grab. I'll play some more with the Torque app today on the way home. Much better understanding of the load applied to the engine now.

Fascinating... Just fascinating...
 

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My commute each day is roughly 155 miles. With that said, I fill the tank on average about every 4 days. I decided to run a test on Mid Grade fuel, and see where the average MPG would go... After running 2 full tanks of Mid Grade, I've seen my average go from 42-43 on Premium, down to 37-39 MPG on Mid Grade..

I have to say I'm really surprised by this.
Keep in mind the Gen 1 engine is intended to be used as a generator, not as an automobile engine. Limiting its function allows the operating parameters to be kept within a range that takes maximum advantage of the benefits of premium gas.

The Gen 1 is capable of full performance using only the large motor, and when the battery is depleted, the Gen 1's range is extended by using gas-generated electricity to fuel the motor. It’s the Gen 2 Volt whose range is extended by transitioning into "gas-hybrid" operation.

Under smooth driving conditions (I think of these as conditions under which cruise control might be used), the generator motor may be clutched to the drivetrain to increase overall efficiency. In Extended Range Mode, shifting into power-split mode provides a path for the Gen 1's engine torque to contribute to the car’s propulsion torque, but by doing so, it also improves the gas generator’s fuel consumption rate efficiency, i.e., better "gas mileage."
 

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Actually, that's pretty good real world data in that screen grab. I'll play some more with the Torque app today on the way home. Much better understanding of the load applied to the engine now.

Fascinating... Just fascinating...
I think there's a few Volt-centric apps that yield much more data. I think mygreenvolt might be one. I'll let others chime in on their favorites. My bluetooth dongle got loaned to a friend and never returned.
 

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I never saw an mpg difference between 87 and 93 octane.
 

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In my 48 years of driving/car ownership, I too have spent many hours trying to out-think the engineers that designed my car. Mainstream marketing and mass production cost puts limits on what is ultimately manufactured.

I'm sure there are dozens of us here that have "improved" our rides with simple throttle-body/carb mods, exhaust mods, suspension mods. Even raising tire pressures above the recommended "comfort" PSI has improved our MPG averages dramatically.

However, I can't wrap my head around why GM would market a car that requires premium fuel if there weren't very critical reasons to do so. In many potential buyers' eyes, requiring premium fuel kills the purchase. Every reviewer has to state the inevitable, "uhh...but...premium fuel required...sorry about that..."

That said, with all due respect, I think the OP is chasing his tail, and potentially challenging the longevity of his engine. ( I have no data to back up this statement;)) I understand the intrigue involved, but strongly believe the engineers have already spent many, many sleepless nights dealing with this, with the bean counters trying to force them to get it to work on 87 octane. They clearly couldn't make it work.

Enjoy the chase, let us know when you catch your tail...or...:D
 

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However, I can't wrap my head around why GM would market a car that requires premium fuel if there weren't very critical reasons to do so. In many potential buyers' eyes, requiring premium fuel kills the purchase. Every reviewer has to state the inevitable, "uhh...but...premium fuel required...sorry about that..."
From my Finnish perspective, I can't understand this. Gasoline prices in the US are cheap compared to my country! Is premium that much expensive as to complain about it in a car that potentially needs very little gas to begin with??

Our "regular" gasoline is 95E10 that roughly matches US 91 octane, and "premium" is 98E5 that roughly matches US 94 octane. Price difference between the two is about 10 euro cents per liter, currently cheapest 95E10 in my area is 1.49€/L and 98E5 is 1.58€/L... And I actually buy 98E5 for my Volt as it countains less ethanol (5% as you can see from the trade name). My Owner's Manual states 95 octane RON or more is required. In that regard 98 is overkill.

I've now owned my 2013 little over a year, and I drove 11050 km in a year. I consumed 46.5L of gasoline, which means avg consumption was about 0.4L/100km or about 588 MPG :)
 

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^ gas may be cheap in the US compared to Europe, but it still costs enough to typically be one of the major expenses of owning a car, so it is worth paying attention to for many US drivers. Also keep in mind that distances are large in many parts of the US. An average US car owner drives 12,000 miles per year, which I believe is higher than in Europe. Along with that, many volt owners are driving a higher percentage of miles on gas than you are.

But I agree it does not make sense to save a little money buying the wrong gas if it could cost more in efficiency and potential repairs. Personally I tried regular octane for quite a while, but am back to premium after noticing my MPG had dropped.
 

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Let's not forget that the car's engine recommends (requires) 91 Octane. I guess one could use less, but given how little gas the Volt Gen 1 sips anyway, why risk it?
 
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