[KarlInOhio]

If it's a older car and you don't care about it as much then a cheaper grade of oil can be used and a cheaper grade of gasoline can be used.

Premium gasoline with a higher octane value is only useful in a high compression engine. If your car is typical it won't get anything useful out of premium no matter how old it is. On the other hand if your car has a high compression engine it needs premium even when old.

I did have one old car that needed mid-range in the summer because it started pinging when hot with regular.

[American Constitutionalist]

I had a car that started to ping because the CAT was clogged up, I had to replace the CAT and no more pinging or more power.

[Smokin' Joe]

Premium gasoline with a higher octane value is only useful in a high compression engine.

I used to think so.

With 87 octane (10% Ethanol) my 1-ton work van gets 15 mpg. With 91 octane (no ethanol), it gets 18 mpg. The 20% increase in mileage is greater than the increase in cost between fuels.

[bayareablues]

How do I know if my engine is high compression?