High Octane Gas?

Turtle n Peeps wrote:

marcsbigfoot20b27 wrote:
As usual, lots of mis-information.

The octane rating of a fuel is its resistance to auto ignite under pressure and heat.
Octane has no bearing on how much energy is in the fuel.
There is no more or less buildup with higher or lower octane.
If you do have carbon buildup, the top of the piston is what causes the problems, not behind the valves. The very tips if the carbon buildup will stay glowing under extreme load or lean burn and cause the mixture to preignite as the piston is going up, then the spark plug fires and both flame fronts meet and bang, detonation and piston damage.
Higher octane prevents the fuel from preigniting.

If an engine is designed for 89 then they have tuned that engine for max spark advance to handle that 89 under most conditions depending on the compression ratio of that engine. If you go wide open throttle up a big hill at 110 degrees with the AC on full blast pulling a 8000 lb trailer, you will probably exceed those parameters due to the high cylinder pressures and temps. Your computer will pull timing so the spark plug fires later, which lowers the cylinder pressures, but also lowers torque.

Therefore in extreme conditions like towing it makes sense to use the highest octane available to keep the fuel from auto igniting from the high pressures and temps. It allows the computer to give you more timing for better torque AND mileage.

A gasoline turbo engine I would use high octane for sure.

Gesus, thank you bigfoot for the correct info!

There are so many incorrect answers in this thread it just makes me :R