MichaelTM

similarly to Octane rating it indicates ignition quality of fuel

ryans4

...my original point was that you can have too high an octane of fuel. My assumption was that if the octane was to high for the motor, you wouldn't get good combustion (which I would have called detonation had I not read your replies, so thanks on that one), i hadn't speculated what would be not good about it.

I was simply trying to point out that there's an upper limit on octane for any particular motor, as it seems many here want to keep running higher and higher. What that limit is I have no idea. Maybe 116 leaded would be great in an S4 (save for the O2 sensors and catalytic converters), I really don't know.

So you say the downside is the stress on the pistons/valves (downside to running to high an octane). Why is that?

MichaelTM

it will keep burning on exhaust stroke, stressing exhaust valves.

So you were right in a sense - there IS too high an octane number for every engine.

MichaelTM

because on too high an octane, peak pressure in the cylinder will be reached later than needed and put additional stress on them

DocSlow (Mini Pig)

Thanks, I'm glad to see that some people on here are still nice =)

Prodigy

******* haha