Why do people equate high octane gas as better gas? It's anything but. Use the correct octane for the vehicle at hand. Putting higher octane in car designed around lower octane doesn't do jack.

Don posted:
> Uhhh, was an elevator, or the bed-covers involved in the story you almost told?

I'll never tell.

Paul posted:
> Wow - I walked into that one!

When I first read this, I was thinking about the elevator comment, and "walking into that one," and now I'm glad I don't work in a multi-storey building.

We now return you to your thread topic, Methane -- er, I mean Octane.

I think it's because performance cars typically demand higher octaine because of their engines, so people make that association. I don't think it's widely understood that octain has noting to do with the energy released by the fuel/air mixture itself, but that it's being ignighted at higher pressure. I think most people equate "Corvette uses 91 octaine, so if I want more out of my Civic, I'll do the same." It's not high-performance gas - it's gas for high-performance cars.

*** Retired after 65,000 outstanding miles ***

Tim,

I can see that. It's funny in most forms of racing there is a rule set against the min octance level and no rule against the max octane level. In F1 most teams strive for an engine with the lower octane to get more energy release.

Just to reiterate a link from the past, this site explains, in layman's terms, all things related to hydrocarbon refining and ratings. Enjoy..

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


Ralph

after reading that, it makes me wonder what the maximum compression ratios are for each octane rating ...

Maybe someone with a lot of racing experience would know. Some of the old cars that I've owned over the years needed higher octane ratings because engines were 10:1, 12:1.... Old Chrysler 383 cu inch, 351 cu inch, etc. with mechanical ignition systems. All of the new cars have electronic FI and computer controlled combustion so even if they are 10:1, you can use reg unleaded 87 with no problems.

Depends on how good the engineers were who designed it, and then followed-up with evolutionary changes. Case in point:

The 2.5L V6 in my '93 Probe needed >91 and was good for for 165HP with 9.2:1 compression.

The same engine in the 98 Contour used 87 for 170HP and 10.1:1 ratio. The SVT version tweaked it further to 200HP.

There is no hard-and-fast relationship- it varies from engine to engine, and year to year for the same engine, as it evolves.

The 2006 HCH is 10.8:1 if I remember right. Guess that's pretty low.

No, it's pretty high, but doesn't need high octane. The higher the compression, doesn't mean the higher the octane of the gas. There are many variables that dictate what the correct octane level should be... compression being just one.