Combustion 101

So what makes the air/fuel explode?  The answer
is electricity. Inside each cylinder is a spark plug.  
In simplest terms a spark plug is two wires whose
ends are held a small distance apart.  This gap is
measured in the thousandths of an inch, and
approximates the thickness of a dozen sheets of
paper.   When the piston is at the top of the
compression stroke-an electric spark jumps across
the gap between the two wires, lighting the air
fuel mix.  Its like the small spark you sometimes
see when you get “zapped” by static electricity,
just a lot more powerful.  

Because this spark occurs every other time the
crankshaft spins, the two wires in the spark plug-
called electrodes-must be made out of a durable
material-in particular the tip of the center
electrode.  They must also conduct electricity well,
and be resistant to the burn and pressure of
combustion.  Traditionally, copper was used.  
Copper is a great conductor, but it is soft-so it is
quickly worn-out.  This is why a tune-up (or
changing the spark plugs used to be regular
maintenance.  Today more exotic materials are
being used to tip the center electrode such as
platinum and iridium.  These exotic metals have
good conductivity but also are very durable and
last 5 or 10 times as long as copper in a spark
plug.  This means that platinum or iridium spark
plugs can last 100,000 miles without wearing out
or “fouling”.  

Increased reliability and long life comes at a cost-
platinum and iridium are extremely expensive, and
such spark plugs can cost 5 times as much as their
old copper counterparts.  However, much of the
added cost is offset when you don't have need a
tune-up every 10-20,000 miles.  The labor costs
of a single tune up are more than you would pay
to upgrade your sparkplugs to platinum or iridium,
and this doesn't even factor in the better gas
mileage you would also achieve.  This is why a
good set of platinum or iridium spark plugs is a no-
brainer upgrade if they aren't already in the
The Timing
The Timing
Spark plug diagram
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