I have seen this come up a few times in different posts and was kinda wondering the same thing. I have a 99 Z28 and it is reccommended I run premium. I realize this is a lot of questions but I appreciate the replies. Thank You.

1) Is the recommended premium 93 or 91(in my area premium is 91)?
2) What would the difference be between running 91 and 89 or 93 and 91?
3) Am I hurting anything by running 89 in my car (longevity of engine, performance, mileage)?

 

The octane rating of gasoline varies depending on what part of the country you live in. At sea level premium is usually around 93 octane, at higher elevations the octane rating for premium is lower. The reason being that at higher elevations the air pressure is lower,so the engine inhales less air than at sea level. This lowers the effective compression ratio, so the engine can get by on lower octane numbers. This makes the oil companies happy, as they can charge premium price for lower octane gas.
If you run on fuel with a lower octane rating than the factory recommends, it will not hurt your engine as long as the Knock Sensor (KS)works properly. TheKS signals the PCM if the engine knocks and the computer responds by retarding the sparkuntil theknocking stops. Running with a retarded spark decreases power and fuel economy. This means that the money you saved by buying cheap fuel will be needed to buy the additional fuel the engine is burning.

 

Okay so basically it would not cost me any more in the long run to use 91 instead of 89 due to an increase in the gas mileage I would be getting, or if it did it would be very minimal, and I could get more power depending on whther or not that knock sensor is working?

 

BP 93 is all that you need. Its the best fuel for your money and people swear by it.

 

If the engine is optimized for premium fuel it will loose efficiency and power if lower octane fuel is used.
If the engine is optimized for regular fuel, running it on premium fuel will not add efficiency or power, but it will cost more to run it.

 

I run 93 or 94 all day everyday. My chevy deserves the best

 

People need to stop cheating their engine by putting lower octane gas than what is recommended. If this is an issue a F-body should not have been a purchase for the gas savers (even though their gas mileage is pretty decent.)

Use premium man

And I live at sea level (Seattle).. and they have 91 here... cheap asses...

 

However there is a race track 40 or so minutes away from home, and right near where my friends and I take our cars to my friends ship with a lift etc. The gas stations there have 94 octane, and I use that when I'm there.

 

But what "premium" is the best to run? Like z28pete said, if the octane is higher than what it is tuned for it won't help, so I don't want to be running 93 if it is tuned for 91 and wasting my money.

 

hmm, here they have a variety, every gas station is different having premium run between 91 and 94. all there regular is 87 tho. i dont think there is a common permium.