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Discussion Starter · #1 · (Edited)
I drive a 1999 Supercharged Regal.

While I'm not sure I can trust its built-in MPG gauge, I do notice probably a 3-4 MPG difference between Regular and Premium gasoline.

They say Premium gasoline (on a car built for premium) will almost certainly get better fuel economy, because the more controlled explosions and no pressure combustion, thus reducing knock. (Or in this case, preventative knock-retardation).

But Premium is getting me LOWER MPG according to this meter.

I'm thinking it could either be an error in how it reads MPG, or I'm thinking the explosions could be less-than-stoich, not having enough oxygen to burn all the fuel.

But this is also my first car and I've only recently learned a lot of this, so I could be way off.
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