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I have a 2013 Volt with 70K miles on it, most of which have been on the plug. I live in Denver, the "Mile High City" and often go into the mountains with it. The Gen 1 requires 91 octane gas but at higher altitudes, the air is thinner so you can actually get by with a lower octane gasoline with most engines. E.g., our other car is a Toyota RAV 4 hybrid requiring 87 octane but I've run it on 85 octane for a couple of years without any knocking or negative effects. But, GM has been very specific on this issue saying that less than 91 octane will damage the engine. So, is there a Volt owner on this forum who lives at a similar high altitude who has used a lower octane gas in the Volt where it has not damaged the engine? That is, someone with a 2011-2015 Volt.
 

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I have a 2013 Volt with 70K miles on it, most of which have been on the plug. I live in Denver, the "Mile High City" and often go into the mountains with it. The Gen 1 requires 91 octane gas but at higher altitudes, the air is thinner so you can actually get by with a lower octane gasoline with most engines. E.g., our other car is a Toyota RAV 4 hybrid requiring 87 octane but I've run it on 85 octane for a couple of years without any knocking or negative effects. But, GM has been very specific on this issue saying that less than 91 octane will damage the engine. So, is there a Volt owner on this forum who lives at a similar high altitude who has used a lower octane gas in the Volt where it has not damaged the engine? That is, someone with a 2011-2015 Volt.
How much are you going to save by not using 91 octane? Will it be worth risking damage to your engine? How often do you exceed the electric range of your car that saving a few dollars is more attractive to you than the possibility of damaging your engine? These are questions that I would be asking myself if I were to consider ignoring the requirement to use 91 octane in my car.
 
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At 1000 feet I'm hardly at Denver altitude. You'll need to use a greater throttle plate opening for the same power up there than I will down here, but the combustion chamber, and the octane need will be the same. The octane number has to do with pre-ignition tendencies, and that has little to do with ambient air pressure from altitude change, particularly since the throttle plate reduces that air pressure to a driver's (or drive-by-wire computer's) demand.
I've been using 89 R+M/2 (mid-grade here) for the 3 1/2 years I've owned it, and hardly ever "top-tier". Don't do what I do because I do it. Do what you think is correct for you.
 

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I live in Denver and had a Cruze ECO MT with the same base engine as the Gen 1 Volt. Even though the Cruze had fuel mapping for 87 octane I discovered I had to run it at 91 to get the best performance. Driving up I-70 west bound on 87 octane it felt like the clutch was slipping, but the issue was the car was pulling ignition timing to protect from engine knock. On 91 octane I never had that issue. In the winter I could get away with 87, most of the time, but I chose to stick to 91 octane year round.
 

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Bob,
I also live in Colorado. In my internal combustion Toyotas (87 octane recommended), I normally run 85 octane with no problem. If I'm towing the camper (especially if going to lower elevation), I'll tank up with higher octane. As you've probably noticed, "regular" (lowest grade) gasoline along the front range starts at 85 octane, but at lower elevations, the minimum octane is often higher (87). In a modern car (knock sensor monitored), I think you can get away with it under most circumstances at our elevation. That all being said... I only have been using premium octane 91 fuel in my Volt. I only burn two or three gallons a month, so the added $0.70 to $0.80/gallon does not bother me. I am not willing to take the risk... If you find yourself driving on gas a lot, you might consider buying premium fuel at Costco which sells the equivalent of Top Tier fuel (though not advertised as such) without quite the cost bite of buying top tier Shell premium.

For those who are doubting Bob, an ICE is a constant volume machine. At 6,000' the atmospheric pressure is 80% less than sea level. The car takes in less mass of air (and will inject less fuel). The resulting charge does not see the same high compression (since there is less mass in the cylinder) and is less prone to detonation. Another "that all being said..." I do recall waking up as a passenger in an 80's K-car that, having traveled from the high plateau of Utah down into the Virgin River valley and then climbing back up, was in the final death throes of constant detonation punching holes through the face of the aluminum pistons. The girl who owned the car seemed to vaguely remember her Dad's admonishment to run it on premium if she ever went below 4000'... at least she won a couple thousand at the casino to pay for the new engine...

The elevation effect does not apply to turbo charged cars which can maintain higher mass charges regardless of elevation and need to adhere to octane recommendations regardless of elevation.

obermd - is your Cruze turbocharged?
 

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It’s been common knowledge here that one major consideration behind the 91 octane premium recommendation is to insure you are getting top tier gas. Because the gas might live in the tank for months on end the thought is get the best to avoid a bad result with low quality and also old gas.
 

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It’s been common knowledge here that one major consideration behind the 91 octane premium recommendation is to insure you are getting top tier gas. Because the gas might live in the tank for months on end the thought is get the best to avoid a bad result with low quality and also old gas.
I just use mid grade 89. In most cases it’s just a 50/50 of 87 and 91 or 93 blended at the pump. It also doesn’t sit in my tank. I use it up within 2 days. I have a long weekly commute that effectively consumes most of a tank each way.
 
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One other thing to note - the LUx series 1.4 engines were designed for 91 octane. The Gen 1 Cruze had a secondary, low octane ignition mapping added so an "economy" car didn't require premium gas. While I wouldn't be surprised if the Gen 1 Volt has the same secondary mapping, just to share the software expense between the two cars, my experience was the engine simply ran better on 91 octane - stick with 91 in the Gen 1 Volt.
 
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I just use mid grade 89. In most cases it’s just a 50/50 of 87 and 91 or 93 blended at the pump. It also doesn’t sit in my tank. I use it up within 2 days. I have a long weekly commute that effectively consumes most of a tank each way.
I will agree with that. On road trips south I usually put mid grade in and save the 30-40 cents a gallon. What the heck it’s getting used immediately.
 

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I live in Denver and had a Cruze ECO MT with the same base engine as the Gen 1 Volt. Even though the Cruze had fuel mapping for 87 octane I discovered I had to run it at 91 to get the best performance.
Wikipedia says Cruze ECO came with a turbocharged engine. The need for higher octane doesn't surprise me at all. Even my low-boost PT Cruiser didn't really like below 89 octane.
 

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I run 87 in the winter when the gas doesn't sit for more than a month, and it is TopTier, the last fill up before spring ill put premium in. I havent noticed any difference in the plugs, valves or intake doing this. Like always YMMV.
 

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Wikipedia says Cruze ECO came with a turbocharged engine. The need for higher octane doesn't surprise me at all. Even my low-boost PT Cruiser didn't really like below 89 octane.
Yes, it was turbocharged, but the engine block itself was rated for 91 octane. GM put this same engine into the Gen 1 Volt, the Gen 1 Cruze LT, ECO, and LTZ, and the Sonic LT and LTZ. The Cruze and Sonic had two ignition mappings, one for 91 octane and one for 87 octane and the car would detect which was in the tank at every startup. One of the big debates on CruzeTalk was whether or not to run 91 octane in our cars and it really came down to "can you, as the driver, notice the difference in your daily driving?" While we told members to test 87, 89, and 91 octane and use the octane level they felt most comfortable at, my recommendation is that for overall fuel economy and engine longevity, go with 91 octane.

Since the Gen 1 Volt's "mule" testbed was the Korean Chevy Cruze LT, I would be very surprised if the Volt doesn't have the same low octane ignition map and the ability to detect the octane at ICE startup.

In my Cruze, one of the glovebox codes was a code that specified 91 octane for the car, even though the owners' manual stated 87. Between my experience on 87 octane and the vehicle coding I recommend 91 for anyone who drives any of the GM Ecotec 1.4 engines, regardless of whether or not it's turbo charged.
 
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Yes, it was turbocharged, but the engine block itself was rated for 91 octane.
It's really not the block that determines the octane requirement, it is the size of the cylinder head combustion chamber which will set the compression ratio for a given displacement. Of course a turbo will add additional mass which further increases the ratio and octane requirement. Many times a manufacturer will put different heads on the same block for different performance needs. Of course the use of lower octane can be somewhat compensated for by changing the timing as you have clearly pointed out. At the end of the day, I would use the higher octane in a Volt. Just don't typically consume that much fuel to be concerned about the higher cost.
 
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That would be correct for a vehicle where you control the throttle plate. On the Volt, you don't control the ICE, the computer does.
And you deliberately missed the next line? "... ....since the throttle plate reduces that air pressure to a driver's (or drive-by-wire computer's) demand."

At sea level and 14.7 PSI ambient pressure a throttle plate opening of such and such will produce a lower pressure ("engine vacuum") at some engine rpm. At altitude with less ambient pressure (lets use the 80% value tossed out there in an earlier post) a greater throttle plate opening will be required to produce that same "engine vacuum" pressure, and guess what? The amount of air present at some engine vacuum at that altitude with that greater opening will be the same as the amount of air at the same engine vacuum at sea level and less throttle plate opening.
The equal amount of air, and the equal amount of fuel injected to use that amount of air, create equal power from the equal combustion cylinder pressure.
All that holds true up to the point of wide open throttle. At altitude WOT will get only so much air. At sea level the same amount of air can be had at less than WOT.
 

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That is not correct. A normally aspirated engine will lose about 2-4% power output for every 1,000 elevation increase.

The engine vacuum is essentially the same at any elevation. As the throttle plate opens, that reduces the vacuum due to there being a greater opening and allowing more air to rush in. At altitude you most certainly get less mass of air drawn into the fixed volume of the cylinder. Less means less fuel can be combusted, hence less power.
 

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It's really not the block that determines the octane requirement, it is the size of the cylinder head combustion chamber which will set the compression ratio for a given displacement. Of course a turbo will add additional mass which further increases the ratio and octane requirement. Many times a manufacturer will put different heads on the same block for different performance needs. Of course the use of lower octane can be somewhat compensated for by changing the timing as you have clearly pointed out. At the end of the day, I would use the higher octane in a Volt. Just don't typically consume that much fuel to be concerned about the higher cost.
You're correct it's not the engine block, but the compression being generated in the cylinder heads and how much they can actually handle predetonation. Since the combustion chambers are cast voids in the block, the overall strength of the block along with the ability of the pistons and the camshaft to handle back pressure that determines how much predetonation can be tolerated. My point was that the Gen 1 Volt, Gen 1 Cruze, and Sonic all contain the exact same hardware (Yeah, GM gave it slightly different part numbers) for this purpose. This hardware, as designed, operates best with 91 octane. It can be made to work with 87 octane but it's definitely doesn't run as smoothly or with as much efficiency. The drop in efficiency was so much that when Edmonds tested a 2011 Cruze LTZ on a 3,000 mile cross country road test they discovered it was actually cheaper to run on 91 octane because of the improved fuel economy. My experience was that on a brand new Cruze ECO MT, I thought the clutch was slipping with less than 1,000 miles on the odometer while driving up I-70 westbound out of Denver. That's how much the car's ECU was adjusting the cylinder ignition timing to protect the engine from predetonation.
 
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I will say that I was driving from Western North Carolina to Atlanta over the holidays. I have a Gen2 Volt. I normally get 37 mpg for the journey. However, I filled up with some non ethanol gas that happened to be Premium, 93 octane. It returned 43.3 mpg. I also noticed that the engine was quieter, seemingly not revving as high as it normally does on Regular, E10, 87 octane. I was quite surprised since Gen2's call for regular.

I'm going to repeat the experiment a few more times and see if it is repeatable.


But to reply to Bob. My question is, on your RAV4 Hybrid, how did you know you were not ever seeing engine knock? Do you have a datalogger or scan tool to see the voltage from the knock sensors?

You can't just rely on hearing knock like you can sometimes in older cars.
 

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I was quite surprised since Gen2's call for regular.
That's a minimum. :) All cars can burn higher octane because they're not diesels and supply their own ignition, but they may just not BENEFIT from it (and its higher cost). If you see benefit, that's good. Keep buying it like you're owning a Gen 1. It'll be fine.
 

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That's a minimum. :) All cars can burn higher octane because they're not diesels and supply their own ignition, but they may just not BENEFIT from it (and its higher cost). If you see benefit, that's good. Keep buying it like you're owning a Gen 1. It'll be fine.
Yep, I come from the ridiculous big turbocharger worlds. 93+ was the name of the game. But, since running Premium on Gen1 Volts was complained about, I'm surprised to have see such a change on the Gen2. Normally, most naturally aspirated cars don't have much of a benefit to running higher octane rated fuels.

However, my experiment has (2) separate variables, 93 Octane, and Non Ethanol fuels. I'll have to do a better experiment to parse out the amounts of benefits that the (2) variables give for these cars.


I'm planning on keeping the 93 non ethanol fuel going. But, the $/mile cost isn't as good as running crap regular. HAHA. But, that extra cost doesn't bother me. It might be $30 per year. MAYBE.
 
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