This article is a continuation of the “Coil Packs” article published in our May 2024 newsletter. To summarize, the previous article eluded to comparing back EMF to the hammering effect when water flow in a pipe is suddenly blocked, then sloshes back and forth making the hammering noise.
So, how does all this water stuff apply to firing spark plugs?
At higher RPM’s the 20K volts sloshing back as back EMF, takes a few milliseconds away from firing the coil a gain. Although most of the EMF can be suppressed with a diode there’s still enough EMF to limit the RPM’s in order to wait for the small amount of back EMF to decay to zero. You can’t have current flowing in both directions simultaneously.
The answer is to fire the coil with a computerized low voltage. They use a chopped 12VDC sequencing each coil in a coil pack, and quickly switching to fire the next coil.
There is no significant back EMF at 12 volts, but there is at 20,000 volts.
As you have noticed, auto manufactures are running smaller displacement engines at high RPM’s using coil packs along with higher compression and variable valve
timing, getting mucho horsepower. Even Cadillac and Mercedes are using four-cylinder engines now. Subaru is getting 271 HP out of a four cylinder engine with a
turbocharger. This is more than the V8 Northstar engine had when it was first introduced at 270 HP. Will the engines wear out faster at higher RPM’s? It seems like they should.
When you were a kid, did you ever imagine a big Cadillac with a four cylinder engine?
Well guess what?
Chuck
For additional information, please contact Chuck.
