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I'm a sucker for pain at the pump.
(lemmy.nz)
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this post was submitted on 13 Jul 2026
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Cars with electronicaly adjustable timing will detect if there is knock caused by pre-detonation/pre-ignition and advance or retard the timing to compensate. So cars that can do both octanes will have the timing more advanced when premium gas is present allowing for more power and efficiency. More timing with lower octane gas will explode earlier than expected causing pre-detonation/pre-ignition.
Engines that have premium requirements usually have higher compression, forced induction (turbo super, charger, ect) or even a more aggressive cam setup that advances timing where variable timing can't compensate or it doesn't have variable timing. So they need higher octane in order to ensure the engine isn't igniting at the wrong time, which over time damages pistons, rings and other components.
Also if your car is not designed for both, you are just throwing money away getting premium if it requires regular. Best case no difference or in the case of my wife's car would actually cause a check engine light.
Ahhh got it, that makes sense. thanks!
VVT isn't really needed for that though, advancing spark can be enough to avoid knock. Although I'm not sure if an engine like that would receive benefits from premium.
Yes I may be confusing the two here I'll adjust
VVT does achieve the goal too, if you close the valves later you'll def. have a reduced compression ratio. That helps avoid premature ignition through compression. (Well, duh..)
But igniting the mixture earlier also helps, probably won't work for engines that are to high in compression.
And forced induction engines with electronic boost control could lower boost pressure, that would also help avoid knock.
At least that's my understanding...
Premium often has a better additive package.