Gas, in my area, is dirt cheap. High level octane is $1.29 per gallon.
Due to this fact I have been using the High level octane and can usually fill my 15 gallon tank for about $18 (U.S.).
FWIW I drive a '97 Pontiac Grand AM (4-banger), and I have not noticed an increase in gas mileage, perhaps better performance from my engine, but not much.
My question, though, in this day and age of high performance motor vehicles and engine strength is it necessarily better on your engine to use the most expensive gas?
Octane is a measure of how much you can compress the gas without it spontaneously igniting.
More compression tends to give you better performace and better fuel economy. Using too-low octane can cause knock. Many enginges nowadays have computers that adjust to octane, so even without knock you’ll get lower performance with lower octane.
That being said, using higher octane than is merited by your engine’s max compression is a waste of money.
The general rule is to run the lowest octane that doesn’t cause your engine to knock and ping. Anything else is wasted money and can potentially hurt your engine.
Because high octane resists premature detonation, it is used in high compression engines. This makes sure the fuel doesn’t combust early in the engine cycle. In a low compression engine (like your 4-banger) there is the possibility that it will not fully combust in the cylinder, but burn downstream, like in the exhaust manifold.
In a properly tuned engine, there’s not need to push the octane higher than recommended. If your engine is running hot or the timing is off, then higher octane can prevent knock and ping, but the real solution is to get your engine fixed.
Small comment -
If your engine can adjust to lower octane, you can still get improved performance running higher octane than the minimum that will avoid knock and ping. Check the tech specs on your engine to see the max octane recommmended (you can run lower without knock, but at the cost of performance).
This has got to be one of the most frequently asked questions here. Please do a search before starting a new thread. To name just one previous thread (from a month ago):
