Octane question
Instructor
Joined: Oct 2021
Posts: 188
Likes: 73
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.
Safety Car
Joined: Nov 2007
Posts: 4,436
Likes: 875
From: Bay Area CA
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.
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.
Exactly!
Safety Car
Joined: Jan 2021
Posts: 3,658
Likes: 1,939
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.
Safety Car
Joined: Jan 2021
Posts: 3,658
Likes: 1,939
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.
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.
Burning Brakes
Joined: Mar 2006
Posts: 753
Likes: 241
From: New Hampshire
Have never put anything but regular in my C4 C5 C6 C7 C8 never an issue. The earlier models with carburetors required high test or they would ping. Consumer Reports did an excellent article earlier this year with a conclusion that premium gas was a waste of money
Pro
Joined: Oct 2013
Posts: 652
Likes: 359
Originally Posted by dinows33
Have never put anything but regular in my C4 C5 C6 C7 C8 never an issue. The earlier models with carburetors required high test or they would ping. Consumer Reports did an excellent article earlier this year with a conclusion that premium gas was a waste of money
Melting Slicks
Joined: Sep 2020
Posts: 2,836
Likes: 2,151
From: Kelso, Wa
BUT if your car IS high compression, it won't get the full power that it was designed to deliver if you don't give it "the good stuff". Sure, most cars these days have knock sensors that will retard the ignition so as prevent pinging, (pioneered by the SAAB TURBO) but apparently there is a limit to that amount in the 2020, and 2021 C8s. One of the minor changes for the 2022 is indeed a reprogramming of that engine performance profile to allow for the use of lower octane fuel without risk of damage. (Can't remember where I read that, but it's out there).
Also keep in mind that this is the same Consumer Reports that, when the Suzuki Samurai DIDN'T tip over when they drove it as they had expected it to do, they changed their test so that I would, then screamed that the vehicle was unsafe.
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Melting Slicks
Joined: Jan 2009
Posts: 2,339
Likes: 2,613
From: Covington LA
Just watched an episode of Engine Masters (California) and they tested a LS3 with 87, 91, 110 and 116. The engine wanted 29 degrees of timing for all 4 fuels and the horsepower and torque varied by less than 2. The C8 is designed to run on 90+ octane and there will be virtually no difference in power between 90 and 93. Don't lose sleep over it. Facts are facts.
Team Owner
Joined: Oct 2004
Posts: 25,583
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The manual clearly states 91 octane is the minimum for the LT2 in a C8. If 87 (regular grade in my area) was acceptable, it would be in GM's best interests to say that and save customers money. They do not because the ECU is programmed for 91 minimum. The manual also states that higher than 91 octane is more desirable because the engine is rated at 495HP on 93 octane. There is no risk associated with using 91, but it won't make quite that amount of max power, which is certainly no big deal for street use.
You can probably get by running 87 if you drive it at half throttle or less all the time, but the manual states you do risk engine damage, meaning moderate or aggressive throttle use is likely to cause "pinging," which is indicative of the air and fuel mixture igniting incorrectly within the cylinders. That can cause internal engine damage.
You can probably get by running 87 if you drive it at half throttle or less all the time, but the manual states you do risk engine damage, meaning moderate or aggressive throttle use is likely to cause "pinging," which is indicative of the air and fuel mixture igniting incorrectly within the cylinders. That can cause internal engine damage.
Last edited by Foosh; Nov 6, 2021 at 11:49 AM.
Race Director
Joined: Aug 2016
Posts: 12,842
Likes: 10,253
From: Garden Valley CA
The original 490/495 HP SAE rating was performed using 93 octane fuel.
It is possible that the 2022 manual is incorrect. Or it is possible that it was determined that the 490/495 HP rating can be maintained using 91 octane fuel.
This would be a good question for Ask Tadge.
It will be interesting when they release the octane requirement for the Z06 engine with an even higher compression ratio.
Safety Car
Joined: Nov 2007
Posts: 4,436
Likes: 875
From: Bay Area CA
Some people will not notice the difference and some people will. It depends on how much timing is being pulled as you go WOT.
Last edited by Mike's LS3; Nov 6, 2021 at 11:58 AM.
Team Owner
Joined: Oct 2004
Posts: 25,583
Likes: 16,942
Until '22, the manual did say reduced power would be the result of using less than 93. That upset people, so they just chose to remove it because it was angering folks not able to find 93, and the small power reduction would be noticed by virtually no one. The manual still states "91 or greater."
That's the only logical explanation.
That's the only logical explanation.
Last edited by Foosh; Nov 6, 2021 at 11:58 AM.
Race Director
Joined: Aug 2016
Posts: 12,842
Likes: 10,253
From: Garden Valley CA
Fact: The 2022 owners manual states 91 octane is the minimum fuel requirement.
Fact: The 2022 owners manual states the engine has 490 horsepower (495 with performance exhaust).
Fact: There is no mention in the 2022 owners manual that fuel with an octane rating higher than 91 is required to obtain the rated horsepower.
Last edited by RKCRLR; Nov 6, 2021 at 12:10 PM.
Instructor
Joined: Sep 2021
Posts: 118
Likes: 62
A engine with 11.5 to one compression won’t run on regular gas without taking a considerable amount of power out of the engine. Engines equipped with carbs didn’t have electronic engine management to retard the timing therefore you would hear the detonation that was harming your engine. The only reason you aren’t hearing the ping in your c4 c5 c6 c7 and c8 is because the engine has knock sensors in it to retard the timing enough so that the worst of the detonation is not audible. This doesn’t mean that you’re not still doing damage to your engine. When detonation occurs what is happening is the fuel is igniting prior to the spark plug igniting trying to drive the piston back down in the opposite direction it’s going, causing a loss of horsepower. In the process it is having a negative impact on the bearings crank rods pistons and rings from excessive pressure. Extreme forms of detonation can break any of these parts. For a guy that has had several high performance cars I would think u would better understand a high performance engine. Give your engine a break and spend another 30 cents a gallon on fuel and you will get some more horsepower in the process. Both of u will be happier.
Race Director
Joined: Aug 2016
Posts: 12,842
Likes: 10,253
From: Garden Valley CA
Detonation is a rapid, uncontrolled "explosion" that happens instead of the controlled propagation of the flame front.
Last edited by RKCRLR; Nov 6, 2021 at 12:09 PM.
Team Owner
Joined: Oct 2004
Posts: 25,583
Likes: 16,942
If that is the case then then GM is intentionally misleading people.
Fact: The 2022 owners manual states 91 octane is the minimum fuel requirement.
Fact: The 2022 owners manual states the engine has 490 horsepower (495 with performance exhaust).
Fact: There is no mention in the 2022 owners manual that fuel with an octane rating higher than 91 is required to obtain the rated horsepower.
Fact: The 2022 owners manual states 91 octane is the minimum fuel requirement.
Fact: The 2022 owners manual states the engine has 490 horsepower (495 with performance exhaust).
Fact: There is no mention in the 2022 owners manual that fuel with an octane rating higher than 91 is required to obtain the rated horsepower.
Last edited by Foosh; Nov 6, 2021 at 12:28 PM.
Instructor
Joined: Sep 2021
Posts: 118
Likes: 62
Technically you are correct. I am trying to simply explain this to a guy that is putting 87 octane in a 11.5 compression engine, but thanks for the comment.
Safety Car
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Reason #20 not to buy a used Corvette
Safety Car
Joined: Nov 2007
Posts: 4,436
Likes: 875
From: Bay Area CA
Just watched an episode of Engine Masters (California) and they tested a LS3 with 87, 91, 110 and 116. The engine wanted 29 degrees of timing for all 4 fuels and the horsepower and torque varied by less than 2. The C8 is designed to run on 90+ octane and there will be virtually no difference in power between 90 and 93. Don't lose sleep over it. Facts are facts.
Just to add about the Manual:
Zormecteon made a good point. If GM reprogrammed the lower timing table to allow for more timing to be pulled, this would allow for 91 octane to be used more safely. Yes, performance will be affected. This would also explain the wording of the 2022 manual for 91 octane vs previous years.
Last edited by Mike's LS3; Nov 6, 2021 at 12:45 PM.