Snakey wrote:
"Phil Kyle" wrote in message
snip.

Bomber Command used to have a "spark plug " crew attached to every squadron,
whose duty was to clean, gap, test and stuff 'em back into the aircraft. I
think you'll agree that was a fairly critical application?

snip
Snakey



yes a critical application, that was why the Merlin engine had two
spark plugs per cylinder, each fired from a separate magneto. In the
section above there was one important stage left out. namely ditch
the rejects after test failure, and failures there were. Spark plugs
do fail, and they also degrade. I used to have to record all fuel
used against miles driven for accounts purposes and as an experiment
i changed the spark plugs separately to the service(I serviced my
own vehicle) new spark plugs gave me about 2 MPG increase tank full
to tank full, replacing standard with high efficiency plugs gave me
just under 3 MPG increase. I had my own small sand blasting kit to
clean my plugs but i still had reduced efficiency on old plugs.
Spark plugs will go on for multiple thousand miles beyond nominal
replacement intervals, however there is a penalty in reduced fuel
economy.

I also used Teflon additives which gave a 1 MPG increase or
thereabouts. that was a use once and it lasted for about five oil
replacements.
Martin McGowan