Depending on the engine, ECU programming, load, and ambient temperature it can make a difference.hatalov wrote:thanks a lot for replys....i was just asking because my friend uses premium in his civic and says it makes a big difference....but i guess it will be the same for me...anyway, thanks for the responses..im beginning to learn a lot.
Some cars have an ECU that can detect knock and thereby retard the timing to avoid detonation with low-octane fuel. This will also reduce power and efficiency when lower-octane fuel is used. Typically, however, even regular fuel will not require the ECU to do this, but on a hot, humid summer day with the car fully loaded there can be a noticeable difference in power from the engine when using regular instead of premium.
HOWEVER, if that is the case, the owner's manual will say something like "87 octane is required, but for best performance we recommend Premium". Also, under most conditions the difference will not be noticeable to the average driver.
That said, your friend's Civic is not such a car (assuming that it is stock and un-modified) and any improvement he claims that he gets from premium is purely illusionary.