I just bought a 2022 cx 30 2.5t. It mentions 91 octane fuel is recommanded for the best performance, but 87 octane compatible. My question is, are there any factual benefits reliability wise for using 91 octane fuel instead of regular? Is 89 octane factually a good compromise?

 

The ECU compensates for the lower octane. the highest potential of all aspect of the engine performance controlled by the ECU and its programing is to use the highest octane available.
As for you need empirical data or prof then have someone that has the means run a Data log comparing both fuels on a test road with all the same operating conditions.
Or you can also use a professional quality Scanning tool do the same test but by looking at such things as timing, knock values, and other engine PIDs and compare using the same test road and conditions between the fuels used.
Or you can do a 1/4 mile run log the results then change octane value and repeat.

The Skyactiv engine is designed, and the ECU is programed to use various octanes however to achieve the overall best performance the higher the octane the better the performance and other operating results.

 

Hi, thank you for the information. I am no mechanic, so I have to admit to not understanding everything that was mentionned, though I think I understand the general idea that the engine and ecu were designed and engineered to use all octane values and adjust in consequence of the used one. Is that correct? As of the me wanting facts, it was more about wanting to know the truth, and not just the "do it because that's what I've always done" of someone who never used octane 91 fuel on a turbo, or someone who always has. I know Subaru engines have had knockings and engine pings that have been associated with lower octane values, so I am just trying to do the right thing, without breaking the buck unecessarily. With that in mind, any additional advise, or do I stick with the above conclusion I got from your previous message? Thanks again for any help.

 

I might also wanna add that I'm looking to pr serve long term reliability, not just short term regular good working. Chatgpt mentioned that that lower octane use could lead to long term premature knocking and other engine symptoms

 

Yes, you have the jest of how the ECU is programed.

yes, there is so much less than the best and supported information about what octane to use. Mostly form the uninformed and those that assume how things work in the physical world .

So to simplify, if you are a daily driver and it's you and one passenger you would be using 87 octane fuels. If you carry a load or 4 passengers and is it no hills or mountains 87 is fine. But if you travel in any elevations more then 3000 ft loaded or multiple passengers you should really at least consider a 50/50 mix of 87 and 91+ gas or just run 91+ gas for that trip If you are going to travel above 3000 ft elevation it is best for the health of the engine to run 91+ gas.
But in any case if you hear the engine pinging then you are either using a really cheaply formulated gas or you need to up your octane level.

BTW running the AC counts as one person added to your vehicle.

 

Hi, understood, thank you for the follow-up! Last question: does the outside temperature matter in this? I live in CANADA, temperature drops below - 20C (-4F) all winter.

 

It does, but it is higher operating temperatures generally when the ambient (outside air temperatures) is at or above 90F (32C) in which case all the operating temperatures are higher and the ECU starts dumping more fuel to maintain the best supportive engine operations.

 

Understood, thank you for everything!!

 

Your welcome.