I know that the topic is for SIs, but I want to now if my 2007 coupe EX could use 87. Another factor to be considered is that my city is located 2600 meters above the sea (less oxigen).

 

As long as the manual says 87 is fine, then yes its perfect to use 87

 

sheesh, a whole bunch of bad information going around here. Almost every modern car specified for higher octane will run just fine on lower octane with NO issues. You might get some worse mileage or power, but not by much in the mileage department.

 

If it's stock, follow what the owners' manual says. I'd bet it'll even run fine on 85 at that altitude. All of my vehicles do, as long as the air:fuel mix is right. You'd really see some improvement by opening up the intake and exhaust to flow more air.

 

Wikipedia:

Higher octane ratings correlate to higher activation energies. Activation energy is the amount of energy necessary to start a chemical reaction. Since higher octane fuels have higher activation energies, it is less likely that a given compression will cause knocking. (Note that it is the absolute pressure (compression) in the combustion chamber which is important - not the compression ratio. The compression ratio only governs the maximum compression that can be achieved). Octane rating has no direct impact on the deflagration (burn) of the air/fuel mixture in the combustion chamber. Other properties of gasoline and engine design account for the manner at which deflagration takes place. In other words, the flame speed of a normally ignited mixture is not directly connected to octane rating. Deflagration is the type of combustion that constitutes the normal burn. Detonation is a different type of combustion and this is to be avoided in spark ignited gasoline engines. Octane rating is a measure of detonation resistance, not deflagration characteristics. It might seem odd that fuels with higher octane ratings explode less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation as opposed to the ability of the fuel to burn (combustion).

 

My rents drivea Mercedes SLK 230 Kompressor and that engine will NOT run on 87 octane and live through the tank. Im sure your right though, most cars would be fine.

 

personally, i look at is as this:

people with way more engineering experience designed these motors, and specified what the motor should use for fuel, oil etc...

I'm going to go by what they tell me...