Has anyone found any FE benefits between different octane grades?

 

It seems to be the concensus that if your car needs regular unleaded, that's your best bet. Higher grades don't help at all, and chemically speaking they actually contain less energy per volume unit.

 

Higher octane gasoline just burns slower, so in an engine designed to advance the timing and stuff, you may see a gain in power, but in an engine designed to run on ~87 it's better for emissions to use 87 since the unburned gas of the higher octane would be dealt with by the catalytic converter, thus wearing it out faster.

 

the higher the octane the slower it burns, this allows with higher dynamic compression engines to ignite the fuel earlier and still get the optimum 5/9 burn by TDC (top dead center), this preempts a detonation event.

If you use higher octane fuel you basically slow down the burn, with two things happening, most ECM's will try to maximize the spark advance for the type of fuel used, so it will compensate a bit for it by starting the spark event earlier in the crankshaft revolution and the other is that because of the slower burn you'll likely pass the optimum 5/9 burn before TDC and will not gain anything out of the earlier spark event. (canceling each other out).

What your trying to do is start the burn and then squish the explosion so that you create the highest cylinder pressure you can from the exploding fuel, this will drive the piston down as fast as it can, and you do not waste any energy during the power stroke, as the piston goes down, the amount of fuel being burned becomes less and less.

Whatever your owners manual states as the minimum fuel requirement to use I'd use that.

Jeff