I had a rough idle when using 89 octane. I switched to 87 and it has gone away. It also seems to have better acceleration.

 

i gotta use 93 or 94....but thats jus cuz i have a turbo

 

I would think that higher octane gas would contain more energy but i guess i might be wrong. The only difference i know that exists between all the different octanes is that the higher you go, the more cleaner the gas is. My friends usually tell me when they put a higher octane in their cars, they have a smoother ride. Well when my evo comes, ill just have to read the owners manual. If it says 93, i go 93. If it says 87, then i pick 87.

 

This is an extremely brief and abridged version of hydrocarbon chemistry; going through the whole gamut of aliphatic and aromatic hydrocarbons, enthalpy, heats of combustion, and additive packages would be a semester of focused organic chemistry.

If you get some gas on your hands and then smell it, the first thing you will smell is a very sweet smell - this smell is caused by the aromatic hydrocarbons in the fuel, which have a very high vapor pressure. The aliphatic hydrocarbons on the other hand are the oily, low vapor pressure, diesel smelling residue left on your hands after the sweet smell is gone.

The aromatic compounds in high octane fuel which give it its desirable anti-knock properties are, because of their chemical structure (benzylic rings and branched structures) less energetic in the combustion process than are their aliphatic cousins.

Hence, the reason why racing gas (and its exhaust) smell "sweet".

 

hmmmmm...Ive read this somewhere before.....

 

hey Dannoh, come join the midwest crew!! www.mitsuclub.tk

 

the lancer calls for 87 so unless you've gone turbo or have new internals then stick with what the manual says. i use 87 and my car runs fine.

 

well... i have been using 93 octane since i first got my lancer which was in october 02... now that i have read this thread i will be switching to 87 octane and saving some money.

thanks for the knowledge DannoH.

 

My friend kept putting 92 octane in her brand new (2000 model year) car. She spent $800 last month to have the injectors replaced- she said the mechanic said the nozzles had 'crusted over' too badly to be repaired, mostly due to the continuous use of a fuel that wasn't combusting fully in the chamber.
Food for thought

 

Here is a short explanation of the basics of fuel chemistry. It is focused on Avgas, but the underlying principles still hold for automotive unleaded.

http://www.chevron.com/prodserv/fuel...rocarbons.shtm

 

So I researched this, and found this site:

http://www.faqs.org/faqs/autos/gasoline-faq/part3/

This is the end-all be-all of gasoline questions.
Let me sum up (and yes, this is contrary to what I have previously stated). Buy 87 octane, just make sure its from a reputable dealer (to avoid "bad" gas).

D

 

From the copious amounts of different reading and research I've done on the forum from the 2-3 good threads on this subject, this whole gas debate boils down to this: High compression or high boost: premium gas (which as we all know has less energy to avoid predetonation under the two circumstances) No forced induction or high compression: regular ol' gas. However, things like timing advance, bolt-on turbos, etc, yes you'll have to move up the octane scale.

 

Ok. This is my follow-up on the whole gasoline octane debate.
I can't claim I am a biochemical expert of any kind, but I can tell you what I've found through my own experience.

As you can see above, my last post was at the end of January, during which I had always used 89 octane. After reading a lot of convincing articles, I decided to try to save a dime, and switch to regular old 87. To be as precise as possible (and because its cheapest) I only purchased gas from the same BP.

After 3 weeks of using regular gas, I noticed that my OZ had a rougher idle, had more engine shake while accelerating with the AC on, and much worse gas milage. I only averaged about 22 mpg with 87 in the city, as opposed to 28 with 89.

Needless to say, I switched back to 89, and plan on using just that from now on. I'll be driving to Tallahassee from Orlando this week, so I'll let you know what te highway mileage is like.

 

Click the Chevron Logo for more information about High Octane fuel:

 

From what I read in the article, using a higher octane can be beneficial, even if you car "requires only" 87 octane.