Anyone know if 90 octane, non-ethanol is OK to run in the C8! I like the fact that it’s non-ethanol, is it better than putting 93 octane with ethanol in the tank?

 

You're better off with 93 octane with methanol. And 90 octane is below what is acceptable.

 

The 10% ethanol is fine in the C8. The ECM will prevent knock by retarding spark - but you will lose some power.

 

91 octane is now acceptable on 2022's, some one posted screenshots of that section in the manual for the last three years models.

 

having the choice which one would you use?

 

Get minimum 91 octane with ethanol over 90 without ethanol. I only worry about using ethanol in my gas-powered lawn mower, leaf blower and weed eater.

 

If you like spending more $$$ for non ethanol, you sure can.

Nothing wrong with 93 with 10% E. Fuel systems for the last 20 years can handle up to 15%, and obviously those with flex fuel capabilities can handle E85.

I would add a stabilizer over the winter if you are not driving the car where you are though.

Power equipment is where ethanol of any content seems to still cause trouble.

 

Sure hope so or we’re all screwed in California
Pretty sure 91 is ok on 2020 and 21 C8s too

 

91 is ok it just sucks power and gas mileage.

 

As others have said, ethanol won't hurt anything on a C8. Comparing 93 octane w/ ethanol to 93 octane without, you'd get slightly better gas mileage with "pure gas," but 90 octane will probably result in the timing being retarded, which will hurt mpg with that fuel, too.

I'd stick with 93 ethanol. That's what the car is designed to run on.

 

That "someone" was me. Here's that post:

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The 2022 fuel system is new and different than the 20 and 21. Use only the manual that came with your car.

 

@Zymurgy Great info. Thanks again

 

Or GM got tired of complaints from people living in areas where only 91 is available The heads, pistons, camshafts and compression ratio haven't changed for 2022.

 

I don't think there is anything new and different that caused the change. The '22 manual entry on fuel was rewritten because of customer angst in places where 91 is the highest one can get, as others have suggested. The part about reduced power was deleted for the same reason. However, the engine will still make slightly more power on 93 than 91. The ECU will automatically adapt to either octane rating and run the engine smoothly. Virtually no one will notice the difference, and certainly not in street use

GM still gets to claim the same 495HP for the LT2 without making a big deal that the rated output is for 93 octane fuel.

 

I posted both my 2020 manual page and the 2022 manual pages a week or so ago. I teased saying it's the same but to keep folks happy who can only get 91 octane they removed the reduced power and fuel economy if 91 was used.

However I searched Octane in the PDF Manuals again just now see a conflict! Not unusual but I do wonder!

2022 Owner's Manual
Pg 178
Fuel
Unleaded gasoline, rated at 93 octane or higher, is required.

P 224
Recommended Fuel
Premium unleaded gasoline meeting ASTM specification D4814 with a posted octane rating (R+M)/2 of 91 or greater is required.


2020 Owner's Manual
Pg 150
Fuel
Unleaded gasoline, rated at 93 octane or higher, is required.

Pg 204
Recommended Fuel
Use premium unleaded gasoline meeting ASTM specification D4814 with a posted octane rating of 93 — ( R+M)/2. If unavailable, unleaded gasoline with a posted octane rating of 91 may be used, but with reduced performance and fuel economy.

My Thought:
Your car your choice BUT I'm now more convinced nothing has changed from 2020 but the wording. Looks to me they just removed the statement that IF 91 octane is used you'll get less power and poorer fuel economy! With 11.5:1 compression ratio it's logical. Back in the day that high a compression required Sunoco 260 or similar than was 100 octane. GM engineers have made a lot of progress with combustion chamber design, aluminum versus steel heads, direct injection, etc BUT can only detune so far, i.e. cut back on ignition timing and use a richer fuel/air ratio to try to eliminate knocking. And <91 Octane could cause engine damage!

 

The one thing that changed was the fuel injection system which gives better city mileage. Maybe that has something to do with it. Also, at higher altitude states only 91 octane gas is available. The main reason at altitude a lower octane is needed is because there is less air to compress.

 

I thought you asked this earlier about using it in your 427 ??

 

For '22, new injectors and fuel pump allow higher fuel pressures, which coupled with modifications to the Active Fuel Management system, allow cylinder deactivation at lower speeds. That why improved city mileage.

The 91 octane language change in the manual has nothing to do with the above. It was done to address continuing owner concerns about not being able to get more than 91 octane, which affects a lot of customers. It's not just high altitude states. Much of the western US, including CA, only have 91 octane widely available.

Output remains the same since 2020, and the earliest models have always been fine with 91 octane.

 

I posted it on the C6 site also. Looking for as much input as I can. As I have the pleasure of owning both a C6/C8. The gas station by me has just started to carry the 90 octane ethanol free gas! Just wanted some opinions on that versus the shell 93 octane I normally use.