Octane Rating

[Greg]

Thought this might be interesting. What octane rating gasoline do you usually purchase? If you buy higher than 87, why? I suppose you might see better gas mileage. Has anyone ever calculated whether their mileage increase offsets the additional cost?

 

[ALLSKIING]

My vehicle requires 93 octaine so thats what I voted. As far as gas mileage, I was always told that 93 burns faster then 87.

 

[andyzee]

Always used 93 until the recent rise in gas prices. Swithced to 87 and find no difference.

 

[thebigo]

I use the cheapest stuff i can find in my car and the most expensive stuff i can find in my motorcycles. I never found a difference in a car, but in a motorcycle you can not only tell the difference between octanes but also distributors. IE: both shell and sunoco far outpreform exxon/mobil, the bikes will barely run on the generic stuff

 

[FRITOLAYGUY]

Unfortunately my car takes Super and is a stick shift, so if i put the cheap stuff it all it does it knock and hesitate, not good.

 

[Hawkshot99]

I was always told that 93 burns faster then 87.

The higher the octane the harder it is to get the energy out of. A engine with a higher compression engine needs the higher octane to work properly, but a lower compression engine(designed for 87) does not need it, and can hurt it. Takes more effort to explode the higher octane.

http://auto.howstuffworks.com/question90.htm

 

[SkiDork]

It's all about the compression.

In my Suburban, 87

In my 528, 93

 

[ctenidae]

Unfortunately my car takes Super and is a stick shift, so if i put the cheap stuff it all it does it knock and hesitate, not good.

Yup. I go with 89, but will fill up with 93 every so often to clean out the pipes. Probably just upsets the computer, but I can feel the extra little kick.

 

[JimG.]

My choice isn't in the poll...

nitromethane.

 

[Greg]

Interesting. I never knew there were engines that required higher octane gasoline; or maybe it's just I've never had a really nice car...

 

[bvibert]

Interesting. I never knew there were engines that required higher octane gasoline; or maybe it's just I've never had a really nice car...

Yup, high compression engines require higher octane to prevent pre-ignition.

 

[SkiDork]

Interesting. I never knew there were engines that required higher octane gasoline; or maybe it's just I've never had a really nice car...

You proly weren't a motorhead in the 60s muscle car era. Thats when high compression was king (except for supercharging) and that meant high octane.

 

[JimG.]

Yup, high compression engines require higher octane to prevent pre-ignition.

In drag racing it's called detonation. For good reason.

 

[Greg]

You proly weren't a motorhead in the 60s muscle car era. Thats when high compression was king (except for supercharging) and that meant high octane.

Not sure I was even born...

 

[skiNEwhere]

I would vote on this but I use 91 octane, which seems to have ran off of the poll.....hmmm......

 

[SkiDork]

Not sure I was even born...

The 60s muscle car era was huge in the 70s and 80s. Now its all that jap crap... Not for me.

Gimme a 69 Camaro with an LS7 any day

 

[JimG.]

The 60s muscle car era was huge in the 70s and 80s. Now its all that jap crap... Not for me.

Gimme a 69 Camaro with an LS7 any day

I owned a '67 Nova SS with a 327.

That came after the "69 Mach 1.

I sold both and my bike after realizing I would surely die in/on one of them.

 

[SkiDork]

I owned a '67 Nova SS with a 327.

That came after the "69 Mach 1.

I sold both and my bike after realizing I would surely die in/on one of them.

Yeah, actually the fastest I ever went on wheels was on my 87 ZL1000 - 140

Sold that to BigKahuna on KZone.

 

[Marc]

The octane rating required to be used for a certain engine is based only on the absolute pressure reached in the combustion chamber.

The more octane in gasoline, the slower it burns, and more ignition energy it requires. The local energy produce by momentary arc of a spark plug is more than enough energy to ignite the highest octane rated gasoline sold a the pumps around the US, so using it in an engine that doesn't require higher octane (typically a low compression ratio naturally aspirated engine) doesn't hurt the engine any, but it runs less efficiently than it would on a lower octane rating. So it's a waste of money.

Engines with high compression ratios or low compression ratios and "forced induction" (mechanical air compression) will yield high combustion chamber pressures and typically require higher octane rated gasoline that takes more ignition energy. As said above, lower octane rated gas in a high pressure engine can ignite before the spark plug ignites the mixture at top dead center of the piston stroke when it should (or a couple degrees before TDC) because of the heat generated during the compression of the mixture. Pre ignition or pre detonation makes the engine run very poorly as energy is being applied to the piston while the piston's (and flywheel's) momentum is still carrying it opposed to the direction of expansion of the gas/air mixture. This slows the engine down, produces a lot of strong and very undesirable forces and will wear your bearings, drive train, gaskets and can potentially bend a connecting rod, valve, blow a head gasket, etc.


Redux: Run the minimum recommended octane rating for your particular engine.

 

[ckofer]

Could you be a little more specific?

It don't mean a thing if you don't hear it ping.