Knock sensors

[RABBITT_Andrew at mv8.orbeng.com.au]

>Dumb Idea forming - maybe.  By knock sensor, I assume we mean
>the knock caused by the fuel air mixture igniting prior to the timed 
>spark - generally at medium load and rpm.  Since this occurs before
>the timed spark, nothing you can do to the timed spark directly 
>affects the knock.  Retarding the spark lowers power thereby 
>lowering the temp/pressure part of the equation - eliminates 
>knock.

this is pre-ignition (which is not the same as knock) and is caused by 
hot-spots on the combustion chamber surface.

Knock is caused by (or so the accepted theory goes - see Heywood for 
the full explaination) high pressure, heat from the charge, and heat 
from the radiation of the flame causing areas in the combustion 
chamber to spontaneously ignite, before the flame front passes thru.

By retarding spark, peak cylinder pressure is reduced, thereby 
removing one of the factors causing the spontaneous ignition.