hyundaitech wrote:

> It doesn't burn as fast. If the engine's compression is low enough it can
> have issues with properly igniting the fuel. If you have a little bit of
> carbon on the valves (an older car), it gets held as a liquid in the
> carbon, and plays having with the cold operation logic worse than 87.
> About 10 years ago, Hyundai had a cold start problems with Elantras,
> carboned valves, bad hesitation for a minute or so. If the customer was
> running premium, it REALLY got bad.

Very interesting; thanks for the explanation. I'm too cheap to run
higher octane fuel than necessary, so I guess I'm safe. ;-)

 

hyundaitech wrote:

> I'd be interested in seeing your comparison. Despite oil company claims,
> everything of repute I've heard indicates there's no performance
> difference with 93 vs. 87 if the engine was designed to run on 87.

Unless he's got a problem with pre-ignition and the ECU is retarding the
timing to compensate, I can't see how one could possibly get better
performance or mileage with premium fuel. I'd suspect this is a case of
the "placebo effect". If he actually IS getting better performance, it
would indicate a problem with the engine or engine management system.