23 civic SI fuel grade question

[NoRebound]

Using 87 octane will cost you about 15 horsepower and about 5-6mpg. It also makes the turbo run harder and hotter, shortening its life. I've run one tank in my '19 Si and it was an awful experience. I hated how the car ran. Yeah, 91 octane is expensive but you bought the car because you wanted a fun ride, right?

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[Naija Bull]

Using 87 octane will cost you about 15 horsepower and about 5-6mpg. It also makes the turbo run harder and hotter, shortening its life. I've run one tank in my '19 Si and it was an awful experience. I hated how the car ran. Yeah, 91 octane is expensive but you bought the car because you wanted a fun ride, right?

None of what is said here is true lol. You don't lose 15-16 horsepower none of that has been proven. There is almost no noticeable butt to seat feel in power loss from my 7 year experience of owning Si's. Also MPG hit is more like 1-3MPG depending on driving habits. Also there is no long term reliability issues, the car will adjust accordingly to protect itself so you'll be fine. My advise though would be try to stick to one grade as long as possible so that the ECU doesn't constantly have to keep relearning and compensating for the fuel changes.