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Possible Duplicate:
What are the benefits of premium (high octane) petrol?
The owner's manual that comes with my car says that I should use the more expensive higher octane fuel for the car. I'm extremely skeptical that I need to do this. Why would I follow this advice? What am I gaining by using the higher octane? What am I risking by using the lower octane?
Yes. You should use the fuel recommended by your owner's manual. If you don't you are increasing emissions, reducing performance and, in some circumstances, putting your car at risk of avoidable problems.
As I said over here:
High octane is required for some cars: e.g., a turbocharged car will likely require higher octane to reduce risk of detonation with higher charge temperatures. High octane is also required to get the optimal power out of a tuned car: properly advanced timing will enhance power and economy (obviously, not at the same time).
Some cars are capable of utilizing the highest octane available, depending on the ECU programming (this is not as common).
Some cars can tolerate a lower octane for an unspecified time by retarding timing. This reduces economy and increases emissions but will allow you to limp home on lesser fuel.
