On 1/7/2017 10:29 AM, John McCoy wrote:
Leon lcb11211@swbelldotnet wrote in news:YPydndGe9p2PjuzFnZ2dnUU7-
:

Cars used to have 6 volt systems but switched to 12 volt so that the
cables could be smaller.

Sort of. The real reason it was done was because tetra-ethyl
lead was invented.

(Tetra-ethyl lead allows higher octane gasoline. Higher octane
gasoline allows higher compression engines. Higher compression
engines require more power from the starter motor to get them
started, which requires more current from the battery. During
the 1950's compression ratios went from ~6:1 to ~9:1, which
became a problem for both the battery and the cables. Hence
the switch to 12 volt electrical systems.)

John



Not sure I follow.

Both lead and higher octane fuels reduce precognition knock. Lead did
not allow higher octane, it boosted the octane. Lead's main feature was
that it lubricated the valves, boosting octane was a perk. Hence in the
early 70's when unleaded fuel was introduced only vehicles with modern
engines could run unleaded fuel with out damage to the valve train.

Knock is caused by a number of reasons, compression being only one of
them. Hotter running engines also create more compression and running
more advance on the spark timing will cause an engine to run hotter.

In the early 80's American built vehicles had relatively low compression
ratio engines, in the 6's, and engine knock was a constant problem.
Enter the computers and knock sensors to retard the ignition timing.