Octane does not matter?

[FourRunner2005]

I've often wondered if I should be putting a higher octane gas in my 2005 V6 4Runner Sport Edition. It says it requires at least 87. In fact, my GX470 says it requires at least 87. As far as I know, octane does almost nothing for you except lighten your wallet. UNLESS you have an engine with some type of forced induction. Supercharger, turbocharger, etc.

"The octane rating is a measure of the autoignition resistance of gasoline (petrol) and other fuels used in spark-ignition internal combustion engines. It is a measure of anti-detonation of a gasoline or fuel.

Octane number is the number which gives the percentage, by volume, of iso-octane in a mixture of iso-octane and normal heptane, that would have the same anti-knocking capacity as the fuel which is under consideration. For example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90.

Knocking (also called pinking or pinging)

 

[pipspeak]

I'm no engineer but I always assumed that:
a) computers in modern engines are able to adjust for different ignition characteristics and;
b) that manufacturers "recommend" higher octane gas for optimum fuel economy. The few times I filled up with 91-octane I swore I got about 1mpg better than with 87. It could have just been a flucke or my imagination, however.


I currently only put in 87 octane (the lowest here in CA) and have had no problems for the last 10K miles.

 

[Thai]

Most of the time, higher octane rating is done to get the most out of an engine (get max HP). This is why you see sports cars "requiring" premium gas more than other type of vehicles.

Personally, i would use premium gas in the 4runner when: towing and possibly at high elevation and going thru mountain passes.

Otherwise, i use the octane that is recommended in the Owner's Manual...87 for Corolla, 87 for Highlander, and 93 for G500. I don't use more or less.

 

[Thai]

Here is more discussion on the topic: http://www.toyota-4runner.org/showthread.php?s=&threadid=683

 

[etom]

There's a supercharger coming out this fall?! How about for the newer V8's?

 

[Jacobzky]

octane does matter for my 110k civic, seems to perform better when fueled with 91 octane.

 

[Casper]

for those of us living in high density altitudes...octane does make a large difference. Timing has to be pulled back quite alot in the summer here in vegas to prevent pre-ignition/ping. Even then on the minimum 87, i still feel and sometimes feel the knock sensors working.

 

[Koz]

Personally, i would use premium gas in the 4runner when: towing and possibly at high elevation and going thru mountain passes.

The higher the elevation the lower octane required but definitely for towing.

Koz

 

[Thai]

The higher the elevation the lower octane required but definitely for towing.

Koz

The octane is lower but you should still use 91 (instead of 93) and above if you go thru the moutain passes...or at least i have been told.

 

[Koz]

The octane is lower but you should still use 91 (instead of 93) and above if you go thru the moutain passes...or at least i have been told.

Usually in these areas the fuel is adjusted with lower octane.

Koz

 

[Thai]

Usually in these areas the fuel is adjusted with lower octane.

Koz

So, at higher attitudes and going thru mountain passes, you get the same performance with lower octance (86 vs. 91)??

 

[Koz]

So, at higher attitudes and going thru mountain passes, you get the same performance with lower octance (86 vs. 91)??

Octane rating is in no way correlated with engine power or efficiency. Octane only has one purpose; to prevent knocking. 86 and 91 octane fuel have almost the same amount energy, the difference is how resistant it is to pre-ignition caused by heat/compression. The higher the altitude above sea level, the lower the octane requirement.

Koz

 

[Koz]

I forgot to give you the reason; in higher-altitudes, a typical NA combustion engine draws in less air per cycle due to the reduced density of the atmosphere.

Koz

 

[Thai]

ahh...cool...no wonder the octane numbers dropped when i visited Colorado. Thanks.