system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Whats the difference between Unleaded and premium gasoline and why can't a car take both?

Just something I've always been curious about but never really understood..
gpt
All gasoline these days is unleaded. Lead was added to gasoline because among other things it cushioned the impact of the metal parts within the engine, reducing wear. Modern knowledge allowed harder car parts to be made so the lead wasn't necessary, and we also discovered that burning lead-infused fuel wasn't super good for our health.

The difference between "regular" and "premium" gasoline is something called "octane". The octane rating of gasoline indicates how resistant it is to ignition under heat and pressure, with higher octane meaning more resistant. Premium gas has higher octane.

Why does it matter? In order to get more performance out of an engine you need to combine more fuel with more air to produce more explosive power. This means you make bigger cylinders (increasing weight) or cram more fuel and air into the same space. Compressing air heats it up, and if your fuel ignites itself before the spark plug sets it off then it can mess up your engine timing and wreck the engine (think a piston flying out through the side of the engine block).

So cars with higher performance engines require higher octane gasoline to work correctly, while normal engines can work just fine with normal gasoline. Regular engines can also burn Premium gas just fine, but the higher octane is expensive so you would just be wasting money for no reason.