87 vs 93 octane

[alanwsx]

I bought my used '19 civic si 4 months before, and I didn't know I have to put in premium fuel until last week. So I drove ~1000 miles with 87 octane. Today I finally used up my current tank, and I put 93 octane in it. I would say the whole car feels very different than using 87 octane. Here is several things I noticed after a couple drives in my usual mountain route:

• When using 87 octane, I felt the car shaking a bit when shifting from 1st to 2nd gear in low speed (~10 mph). Using 93 octane there is no more shake, and shifting between 1st and 2nd gear became smoother because of this;
• The engine sound is different. Using 93 octane, the engine sounds more bass-heavy than 87 octane;
• The car accelerates more effortlessly in 3rd and 4th gear. (I'm not sure I like it or not because I do enjoy the engine power coming out suddenly at ~3500rpm)

I remember reading some posts in this forum saying that there is no different in engine performance between using 87 and 93 octane. I think that impression is wrong in my case.

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[gtman]

I remember reading some posts in this forum saying that there is no different in engine performance between using 87 and 93 octane. I think that impression is wrong in my case.

Premium is recommended by Honda for the Si. I wouldn't recommend using 87 at all for performance.

I think you might be mixing up the Si octane info with the non-Si turbos. Honda recommends regular gas for those. Unless tuned, those models won't see a big difference with premium.