I would like to better understand how the spark travels. Thanks in advance.

 

The coil has two magnetic windings in it: Primary and secondary. The primary circuit is switched in some fashion or another - in the old days it was mechanical points, now it's an electronic circuit that is triggered by a sensor (that is a topic unto itself, but you asked about spark, so we'll go on). When the primary circuit of the coil is powered (battery or alternator voltage), it creates a magnetic field. When the power is switched off, the magnetic field collapses into the secondary circuit, which has a lot more windings in it than the primary circuit. As the collapsing magnetic field passes through the secondary windings, it creates voltage that is much higher than that which was passed through the primary winding.

Electricity is lazy and will go through the path of least resistance looking for a "ground". The secondary coil has a terminal, and the electric voltage passes to it. This terminal is connected to the rotor (in distributor-type engines - assuming that's what you have), which is turning toward the distributor cap terminal for the cylinder that is supposed to be ignited at this time. There is a small gap between the rotor terminal tip and the cap terminal, but that is the easiest path for this lazy electricity, so it jumps to it.

The cap terminal has the spark plug wire attached to it, which in turn is connected to the terminal on the end of the spark plug. This is connected to the center electrode in the spark plug through the middle of the ceramic insulator. At the end of the center electrode, there is a gap to the ground electrode that goes to the metal body of the plug, the "ground" the electricity has been seeking all this time. Jumping that gap creates heat, which ignites the fuel/air mixture that has just been compressed in the cylinder.

In a V8 engine, 4 sparks occur for every turn of the crankshaft. When your tachometer says 3000 RPM, that is 50 crankshaft revolutions per second, so your coil is sparking 200 times per second.

Impressed?

------------------
82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam and intake, World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back).
57 Bel Air, my 1st car. 0.030 over 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlock header mufflers, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, LT MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Best 15.1/95.5 @ 5800' Bandimere.

 

Yes. Very thorough.