I did a great deal of technical reading on the subject of the flame front. I got curious because of this particular thread and had some spare time. Flame front is affected by so many things; for example piston speed, squish area and combustion chamber shape, plug location, compression ratio, swirl, mixture ratio, temperature, RPM, throttle opening, engine load, cylinder deposits, the timing, and last but not least, octane. Keeping a performance engine on the cutting edge is an engineer's nightmare.
Even an engine designed to run on say for example, 91 octane... may well need 92 octane soon enough because of deposits in the combustion chamber and on the backside of the intake valve. It's amazing how quickly these deposits begin to form and how even little things like that can and do change the octane requirements of an engine. That's one of the reasons guys have become so fond of putting a catch can on engines like my 392 HEMI. They reason that oil mist being pumped back into the intake through the PCV valve surely contributes to these deposits.
One of the big issues we have as back yard "tuners" is that it's so hard to determine just how much octane is actually enough. Even if we escape the "more has got to be better" myth, how much is just right? We typically don't have any gauges to help us determine just when the ECU begins to retard timing to negate detonation. We get to guess at this much of the time. And that's where all the disagreement comes from. We find ourselves at the mercy of the manufacturer's recommendations, and the oft-times uninformed opinions of others. But I wonder:
Wouldn't it stand to reason that when manufacturers set their "recommended fuel grade" for a given engine, that they might just add in a little bit of cushion to their recommendation? If engine "A" only needed 90 octane to run properly, what's to stop the manufacturer from recommending 91 octane to cover their behind? Maybe, maybe not. Just musing a little here...
Gary