Quote:
Originally Posted by chris719
Yeah, although these days you never know what ECUs are working in a sort of adaptive range where they will advance timing if possible under certain conditions. It seems like some BMWs will do this if you run higher octane for a while. I wouldn't expect a Subaru base 2.5L NA engine to gain HP from 100 octane, but you never know if they benefit a little bit up to 91 or 93 despite being rated for 87.
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I think in general ECUs limit the car to the rated/designed HP. This means when you put higher octane in, it "doesn't care". It doesn't try to do anything with this at all. If you have a tune, and especially if you have a turbo, you can take advantage of this, but otherwise, it just "doesn't care". The cams won't support more power and it just doesn't care.
The whole thing about "higher octane doesn't benefit" is limited to those lower performance cars and the people that buy high octane for them. My Hyundai Elantra GT N-line was specifically designed to give max performance on "regular". A little 200hp 1.6 turbo-4. With a tune and a couple mods like wastegate solenoid and boost control solenoid, I was running it on premium and it ran well, but then I was asking a little more out of it than stock. Stock, it didn't care if I put premium in or not, that's how they designed it. Cars like my SS 1LE or Stinger, they crave pretty high octane. Lower octane makes a noticeable difference.