[ST] "pinking" and mpgs

[Les <chopzooey69@xxxxxxxxx>]

"pinking" shears.  remember those from grade school?

it's my unprofessional understanding that the sound of detonation
is the sound of the pressure-wave-flame-front expanding from the
vicinity of the spark plug colliding with the pressure-wave-flame
front expanding from wherever the preignition got started.  The
two waves impact each other and go ping!  Or pink!  Or knock!
Depending on where the listener was raised.  Schroedingers's cat,
etc.  It's not necessarily the sound of preignition pushing the
piston downward at the wrong time.  Actually, i seem to recall,
the increased pressure/temperature ahead of the advancing desired
flamefront tends to trigger the undesired combustion in the remaining
unignited fuel/air mixture.  It gets further squeezed, as it were,
and can't take it sitting still.

also, i doubt that "extra octane" is going to decrease efficiency
or power output in any measurable fashion.  i use premium for the
extra cushion effect...afterall it's only ten cents more per gallon.
I still sometimes hear a little "spark knock" when launching hard
away from a stop (as in lofting the front wheel) when the engine
is really hot.  Do our Triumph engines actually have a knock sensor?
I've never heard of a motorcycle with a knock sensor, but I've been
rather out of the loop with the technological advances of the last
decade or so.  Without a knock sensor, there is certainly not going
to be any increased power from higher octane gas, I will admit, but
i feel that 40 cents per fill is worth the extra peace of mind that
i'm not going to inadvertantly soften the tops of my pistons.  Who
can really hear pinging with earplugs in going 80mph in the wind
anyway?

i was thinking about how we measure miles per gallon and decided 
that on a single tank, differences of less than 1 full mpg are not
really significant.  the slight differences in angle of the bike 
during fueling (due to not-perfectly-level pavement in the station)
and the unrepeatability of any exact level of "full" due to 
different temperatures of the fuel (it expands and contracts quite
a bit, you know, which is why in aircraft we measure it by weight
not volume) put any fractions of mpg within the margin of error.
i forget the terminology for that in chemistry.  you can't expect
more precision in your results than the precision of your measurements
going in.  that.  anyway, i figure that one "full tank" can easily
be more than half a pint different than another "full tank" and that
can throw off the mpg calculation by over 6/10ths.

All than being said, i've always used shell brand and have never seen
less than 39 mpg on a tank, but most recently i used "slaveway" brand
and got 36.  makes me go "hmmm..."  there was no alcohol in this gas.
probably it was just all the short trips on rich mixture and the idling
in traffic on this particular tank.

i think i'll make myself another drink now.  

--Les
Seattle
'02 ST BRG (the fastest color...extra boost from absorbing most
higher energy photons yet cleverly pinging a precise blend of
blue and yellow wavelengths.  this is why jaguar won more races
back when, you know.)









		
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