[darkpuppet]

jcarle,Feb 3 2006, 01:07 PM Wrote:As for the 94 octane, I'm damned curious to know what difference it makes good/bad or otherwise to use 94 or 87.
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Actually, higher octane can actually impede performance because the flamefront moves slower. This is great if you have more advanced timing or other modifications that would normally introduce pre-ignition.

On my stock zetec, 87 Octane was getting nearly 70km more on a tank than 91 over a 3,000km round trip.

There are people that say running high octane on a low octane engine may result in octane dependence as carbon may build up in the engine that would introduce knock with lower octane gas over time... but I don't have first hand experience with this.

The unfortunate part of 87 Octane is that it's the bottom of the barrel gas.. the gas that doesn't pass muster for anything else.. so it may have impurities that higher octanes don't have. I've never had a problem with 87 octane per se, so I can't quantify any possible harm running 87.

To be honest, the two things a stock NA focus motors need least are spark plugs and higher octane gas. They may not do any harm, but I honestly don't think they're doing anything positive either.