The Volvo Parts, Accessories &
Performance Specialists Since 1963

Spark Blowout or is it My Birthday?

2011-01-05 - IPD Staff

Somehow in this day of skepticism and disbelief we have allowed a sneaky little myth to arise and take hold of a position in the ranks of car enthusiast vernacular: Spark Blowout. Well...perhaps not a myth, but a misnomer.

I’m not sure what this is supposed to mean but I hear it all the time. I can see where the term came from, as the phenomenon tends to rear its head when adding boost, and it's easy to think of boost air from a turbo blowing out the ignition spark like it was a birthday candle. 

But a spark isn't a flame, it's an electric arc, and electric arcs cannot be "blown out": at the moment of combustion, the air and fuel in the cylinder isn’t moving very quickly when compared to when it enters the cylinder via the intake valve...and with the valves closed and the piston up at top dead center, not much "blowing" is happening. At that critical moment, the ignition coil fires, and spark plug passes the spark across its electrodes and kicks off combustion, *kablam*.

Spark blowout is really a lack of electric arc forming between the spark plug's electrodes. With high compression or high boost, we're packing more molecules of fuel and air into the same space, and since air and fuel aren't all that conductive, this increases the dielectric (insulating) strength of the air/fuel mix in the cylinder: when the dielectric strength rises beyond what the ignition coil and spark plug can blast a spark through, we get spark blowout. Ionization voltage is the initial voltage your ignition coil needs to strike an arc across the spark plug's electrodes, with the lower voltage required to keep the arc going through the ionized air called the burn voltage

The bottom line: dielectric strength is how much ionization voltage is needed to jump the gap and make a spark, and a denser air charge or a wider spark plug gap will both raise this dielectric strength. If you're not careful, they'll raise it past the voltage your ignition coil can support, and you get spark blowout: no spark.

So, how to combat ignition misfires due to high cylinder pressure? First make sure your cars ignition system is in good shape. In addition to fresh, correctly-gapped plugs, if you have a distributor ignition car you should consider a new cap, rotor, and plug wires. Consider replacing the spark plug wires with performance wires and the stock coil with a high output coil like the IPD MSD coil kit. You’ll find that these performance upgrades will make the difference between a high performance car and a reliable high performance car.