Octane? I did a search

[rover4x4]

SO what does the octane rating really mean? I was asked the other day and couldnt provide and answer, the higher the better/cleaner etc was all I really knew. Does it burn different or what? what really makes one better than the other, something like that anyways????

 

[Tim_H]

http://chemistry.about.com/cs/howthingswork/a/aa070401a_2.htm

 

[rover4x4]

cool

 

[Jparker]

The higher the octane rating, the more knock resistance there is. Knock is pre-mature ignition, the mixture in the cylinder exploding before the piston is in place because of high temperature and pressure.

 

[GregFrench]

Supposedly, the computer can detect what octane you are running and will adjust the engine to run on it.
Sounds like Foo-foo to me.
What if you mix octanes? What then, Mr. super computer?

 

[Off Road Disco]

Sounds like Foo-foo to me.
What if you mix octanes? What then, Mr. super computer?

My guess (and only a guess) is that you would get a blend of the two and the resulting octane would be something in the middle.

Computers can deal with variables. They just don't do well with lots of heat or moisture.

 

[GregFrench]

Yeah...I was joking. I know computers can do all of the aforementioned things. I just don't like them. They're great when everything is working, but how often does that happen?

 

[MUSKYMAN]

octane is the rating used to calibrate the burn speed of gasoline

the higher the rating the slower the fuel burns

lower octane gas has more stored energy then higher octane fuel

but higher octane is needed in higher compression motors running more ignition advance

this is why you will hear that the best MPG comes from the lowest octane you can run without pings and knocks

MM

 

[p m]

Computer?

Greg,

all the computer can do is to use the input from the knock sensor - and retard timing until knock disappears. With the spark retarded, the engine feels more sluggish and less responsive - therefore, you'll likely see worse gas mileage on lower-octane gas.
It does not contradict Thom's last statement - you _could_ get more power if there was no detonation.
It is actually a very simple feedback loop, much simpler than the other ECU tasks. You can retrofit older vehicles with a knock sensor and ignition control circuit.
The difference can be substantial - my old '68 Wag's Buick 350 would run beautifully with 5-7deg of initial advance on 89-grade gasoline, ping like crazy on regular, but if I retarded the ignition to originally called-for 0 degrees, it would feel like a 4-banger. Having a knock sensor and ignition feedback would've helped a lot.