I like what you've written Reptile but whenever I've read about the whole 'flame front' thing with regards to KR I'm a little foggy. Another way I think about KR and timing is that fuel takes time to burn in the cylinder. Once combustion begins and starts to spread you will reach a point of peak combustion. Ideally you want this to occur slightly after the cylinder reaches TDC. If peak combustion happens before TDC you get Knock. Imagine your piston racing towards the top of the cylinder and before it gets there it runs into the meat of the fuel burn explosion. All of a sudden the force of peak combustion is trying to force the cylinder down and yet the mechanical makeup of the engine keeps forcing the piston up. At some point things are going to break. Anyway, that is why timing is retarded as one way to combat Knock. You start the combustion later to allow peak combustion to happen after TDC.
That is a picture I can get in my head. It helps me understand timing with relation to what I want to achieve with tuning but also how I would want to use it to battle KR. KR is actually the PCM retarding timing to accomplish this.
I need to try to get my head around the part about higher octane not burning slower, though. My understanding has always been that higher octane fuel has a more controlled (hence slower) combustion. That's why it helps combat knock. It allows the peak combustion to occur after TDC. Just a different method to get to the same place as retarding timing. I'll need to re-read your section on octane and burn rates and why higher octane reduces Knock a few more times.
Thanks for doing this.
