Patman

Before I got my 2018 I was under the impression that the owner's manual in the Canadian spec C7s listed 91 octane as the recommended fuel, so I was all set to run both Costco 91 and Shell 91 in my 2018, both of which are ethanol free up here and Top Tier. But after reading my manual, I see that our cars up here also list 93 octane as the recommended fuel, but that you could run as low as 87 but performance will suffer.

So my question is, given the options that I have up here, what would you guys recommend I run? I could run the ethanol free 91, or I could also easily find Top Tier 94 octane at most Petro Canada stations here, but that has 10% ethanol in it. Will my performance suffer that much if I ran 91 octane? Or am I worrying too much about running a fuel with 10% ethanol in the first place? (either way, I would definitely make sure to run the ethanol free stuff for winter storage)

dashotgun

all we get is 93 octane with ethanol here it would not be a problem. OTOH the computer is set for 91 why run higher octane if not needed?

GS1960

Being in California, we get both lower octane and ethanol. If I remember correctly, ethanol has a slightly lower flash point so does not give you the same explosion as with true gas. I am not a performance driver, by any stretch of the imagination, and I get all of the performance I want. Try the different fuels and decide which one you prefer.

Rebel Yell

Pat, I run Shell 93 w/ethanol as a rule. But, if I'm on a trip and can't find Shell I'll use another top tier brand. As I understand the manual we should only use 87 in an emergency (if that's all you can find), and just enough to get you to a place you can get the 93. In my previous C6 I tried 93 non ethanol while on a trip. The mpg's were better, but not enough to make up for the increased cost of the gas. As far as performance with no ethanol I see no need to worry about that unless you're tracking your car. Modern engines are designed to run a 10%, or less ethanol blend.

Motors5

In Sweden mimum octane is 95, there is also 98 and 98+ available. I use 95 most I f the time but 98 during track days.

Morors5

Patman

That's the beauty of our Costco up here selling non ethanol premium, not only do we get the benefit of slightly better MPG, but it's considerably cheaper than premium from any other gas stations up here too. So it's a win-win, I'm just wondering if I might lose some performance with the 91. But if in fact it is tuned from the factory to run on 91 that would be perfect. At the same time, if I'm only going to lose 5hp by running 91 vs 93 or 94, I'm ok with that.

LDB

For an unsupercharged engine, the power difference for 91 versus 93 octane won’t be noticeable without a stopwatch. The mileage loss for 10% ethanol will be about 3%, or 1 mpg. Some people feel strongly about the politics of ethanol, but that’s your choice. All the fuels you mention are top tier, so that’s not an issue. There are no serious risks to ethanol for a modern car. Even if you store it over the winter, ethanol does not increase the probability you will have water separation. It only means that if you are unlucky enough to run into the circumstances that cause it, the problem will be slightly worse with ethanol. But a few bucks worth of stabilizer will prevent that from happening, so it’s not a killer issue. Just be sure that if you do store it with gas containing ethanol, you don’t use an IPA-based stabilizer like Seafoam. IPA-based stabilizers will not prevent water separation if ethanol is present. Bottom line is that none of the fuel choices you describe clearly and obviously beats the others. It depends on how you balance out the small power difference, the mileage difference, the price difference, and the politics of ethanol.

Patman

Thanks for your input! So now that I know I can safely run 91, I will seek out Costco whenever possible, but there is a Shell station a couple of miles from my house that I like as they price themselves about 5-7 cents less per liter than everyone else. There is a good chance I will take this car to the dragstrip from time to time, and for sure during those occasions I will run 94 octane just to be sure I'm getting little or no KR to spoil the fun

John Harry

I believe that all EU countries use the RON method of measuring octane, while the US uses (RON + MON) / 2. So your choices of 95 or 98 are equivalent to US ratings of 91 and 93.

TEXHAWK0

I would not run less than 91 octane except for when there was no other choice.
Most modern fuel systems can now handle 10% ethanol with no adverse effects (like corrosion), and as you know the ethanol actually increases the octane rating. The disadvantage is that ethanol has a lower fuel value and your gas mileage will be less so you would be sacrificing fuel mileage for insignificant gains in performance.

Avanti

Go with the 94 and don't bother looking back... DRIVE & ENJOY!

LDB

One caveat, once the knock sensor triggers a bit of spark retard, while the ECM keeps trying to go back to clean timing, that return to clean isn’t instant. I don’t know how quickly it drives things back, but if you’re serious about seeing the small 91 to 93 difference, you should probably run a few tanks of 93 to get ready, not just fill it up with 93 on the way to the drag strip.


This is a very picky point, but while ethanol does indeed have a high octane number (about 108), fuels are blended to the octane spec on the pump. So for example, a 91 octane fuel with 10% ethanol does not have higher octane than a 91 octane ethanol free fuel. The fact that the 10% ethanol fuel gets a boost from the ethanol is cancelled by the fact that it won’t have as many other high octane components. So from a performance standpoint, all you see from a fuel with 10% ethanol is the roughly 3% drop in mileage. There is no power gain from the ethanol’s octane since that is washed out in the blending process. The mileage drop is not washed out since ethanol contains less energy than the various normal gasoline blending components.

4thC4at60

I've been running ethanol 10% in Corvettes for more than 700,000 miles - ZERO problems.... don't over-think this....

TEXHAWK0

True, 91 octane is 91 octane. Just pointing out that when you use ethanol to increase the octane instead of another component, you are sacrificing mileage.

LimaCharlie

I would use whichever was cheaper. If you really want performance, go to the airport and fill up with high octane avgas.

C82LT

95 and 98 in Europe is equivalent to 91 and 93 in the US.

Thunder22

Isn't octane calculated differently in Europe than in the US?

Patman

That's an excellent point! I remember when I had a brand new 98 Firebird Formula, with that car we found out that if it goes to the "lower octane table" due to those KR events, it would stay on that table until you added about a 1/2 tank of fuel or more. Once you added that fuel, the computer would assume you've put in higher octane again, and return itself to the "higher octane table" But a lot has changed in 20 years, so someone on here who has logged a lot of time with a scan tool hooked up to their LT1 would probably be able to explain what they've encountered here.

When exactly was ethanol widely introduced in your fuel in the US? I know that they only first started experimenting with adding ethanol to fuel here in Canada around 1996 or 1997 but it wasn't really fully implemented until a few years after that.

Foosh

Yes, see post #9.

Crossed Flags Fan

I use the highest octane AND whatever TOP TIER gas station is around when I need to fill up. ONLY USE TOP TIER gas and forget about any type of additive! http://www.toptiergas.com/licensedbrands/