I just sent a post asking Lynn to explain the .010 gap.  I still had his original e-mail in the in-basket and have just re-read it - I don't understand the reference to "secondary ignition breakdown" and "secondary breakdown" in the 2nd paragraph, "One quick check for secondary ignition breakdown, is to quickly install two new plugs in the leading holes, gapped at .010". If the problem is still there, it is less likely the secondary output. If the problem is gone, it is likely the secondary output."

 

Please help an old timer used to "coil and distributor ignition systems" who is a "first time owner" (and VERY HAPPY user) of a modern (1993 & 1995 Ford Escort) ignition system:

. . .  Are these new "igniter blocks" still using the "primary"/"secondary" coil principle of the old round coils?  If so, what makes these 1990's and later "high energy" systems "higher voltage"?  Higher ratio of primary to secondary coil windings? (or vice versa?) and/or the totally mysterious "ignition modules" that go along with the coil packs?  I.e., are the square coil/igniter coil blocks doing the same thing, only better, than the old coils?

. . . If so, then is Lynn's ref to "secondary ignition breakdown" a ref to some kind of failure or degradation of the secondary coil windings? (such as internal shorting of sec coil windings to each other, so as to reduce "effective" number of coils in secondary; or, arcing of secondary to engine mount/block) so voltage to plugs is significantly down?)

 

Also, why put the .010 plugs only in the leading holes, as opposed to trailing, or both holes?

 

David

The first ignition systems I saw were points systems using a capacitor across the open points to prevent arcing and short points life. This is a great system with 30 billion or so installations working just fine. Cars, tractors, airplanes, lawn mowers, everything.

 

Then we want to go faster and make more power with higher compression and more revs and the trusty Kettering system starts to have problems.

 

The time it takes to build a full flux field in the coil is a function of a number of built in features, and some outside stuff such as battery voltage. One trouble shooting item that you learn early is that secondary ignition breakdown (anything that reduces high voltage performance) is greatly affected by battery voltage.

 

When the generator on the 40 Ford dies at night and things start to get dim on the way home, you jump out and pull off a headlight wire and down the road a bit the engine will no longer take full throttle, but will run OK at a lower throttle setting. Sometimes you make it home and sometimes you don't.

 

So you cannot get full voltage (energy) from the coil if you don't put in enough voltage (energy). You know now that higher cylinder pressure requires more secondary voltage, and full throttle means higher cylinder pressure. So when you back off of the throttle a bit and lower the cylinder pressure, the engine runs fine again.

 

So supply voltage and cylinder pressure affect secondary voltage performance. Cylinder pressure would include higher compression ratios, turbo or supercharging, adding more carbs, wilder cam profile, and all of that other stuff you did. Voltage is obvious, less in = less out. Too simple maybe?

 

Rise time (time to full field saturation) is a function of construction, core volume, lamination count and permeability, wire diameter (resistance) inductive reactance, turns ratio, container material and shape and hundreds of other features that a coil engineer would talk your ears off for hours telling you about. Rise time in coils and capacitors function in accordance with the 62% rule. However long it takes the coil to charge up to 62% of it's full field capacity, is one time period. So when you establish that period of time, the coil will require another of those time periods to charge to 62% of the 28% of remaining capacity. This rather sluggish performance is the same for all coils, and capacitors everywhere, all of the time, even in California.

 

So if you want more performance from an ignition system you have to come up with a way to cheat the system. Thicker primary wire for the 40 Ford? Yes. A coil with a higher turns ratio and thicker low voltage wire? Yes. A laminated coil core instead of a solid slug. Yes, and on it goes. An 8 volt battery? yes to everything.

 

But the rise time may be faster but it is still subject to the same rule. So if you want more revs and the rise time of the coil is starting to limit secondary voltage, you keep at it and then you come up with dual point distributors. So more time is spent with power supplied to the coil. Simple. You may also have noticed that no coil or capacitor ever gets to be fully charged. No matter how long you work on it, even forever.

 

One problem is the points themselves. Noisy, bouncing, high resistance, attracting dirt and oil, requires a capacitor to stay alive, wear out and need adjustment and so on.

 

So, the Transistor is invented (by my friends at Western Electric (Bell labs)) And then the SCR Silicone Controlled Rectifier (big high current Transistor) and somebody says look at this. If we figure out a way to tell this thing when to do it, we could switch off the coil primary and eliminate the points. And they did. And then the points system was relegated to the lawnmower.   

 

The electronic switch does wonders for a Kettering system. Allows longer power on time to the primary, ( like the dual point distributor) so coil saturation is always higher before field collapse. No point noise broadcast into the radio. And in the early days they switched it with the same old points.

The points just carried just a few volts and little current so they didn't wear out quickly and so on.

 

Then came induced triggering from an optical source and shutter wheel, or a magnetic trigger. No no parts touched any other parts, so nothing could wear out, and a tune up was limited to plugs and wires.

But the coil is still limited to the 62% rule. And if you want to scream a multi cylinder engine rise time still limits high voltage output. But at low speeds, you can use bigger plug gaps and get better mileage.

 

The piston engine drives the fuel air mixture toward the spark plug(s) and the possibility of some of it not lighting is slim. The rotary moves the fuel air mixture past the plugs at 150 miles an hour, and the possibility that some of it won't burn is excellent. The rotary also has virtually no squish area and a large cold low compression combustion chamber. All bad mojo.  

 

So anything that adds fire (energy) to the combustion process is a big help in a rotary.

 

So, you know the coil rules now, so how do you add energy at the spark plug?

 

The 8 volt battery (The cheater battery from the Ford tractor for cold weather starting) helped the 40 Ford street racer.

 

Wow, 24 volts really makes a great high out put coil and cuts the rise time way down.

How about 400 volts? What would that do? Where could we get that much? Well, in the lab, 400 volts to the primary windings cuts rise time to nearly nothing, so you could have great high voltage performance in a V-12 engine turning 10,000 RPM. Unlikely to be needed, but you could do it.  

 

So, through electronic trickery a free running mono-stable multi-vibrator circuit (two transistors) generates sort of a fake square wave AC that drives a transformer that steps the 12 volts up to 400+ volts, that is fed to a rectifier (to turn it back into DC) to charge a large high value capacitor, in a very short (rise time). When ignition is called for by whatever triggering device, A large SCR connects the output of the capacitor to the coil primary. This 400 volts surprises the hell out of the 12 volt coil and the coil delivers about three times it's rated output to the plug, and anyone standing too close. There you go. A high energy system.

 

The very short rise times aid in firing dirty or fouled plugs before leakage paths are found to short the plug by establishing a path around the gap.

 

The leading plugs in the rotary deliver the spark that does most of the work. So loosing the leading system makes about a 25% loss of power. The trailing system helps out a bit on power, and helps with emissions, so loosing that system makes about a 5% loss in power. So many trailing systems fail and go unnoticed for years. 

 

If an engine stumbles and reducing throttle slightly, returns smooth running, the first thing I think about is voltage to the ignition system.

 

Lynn E. Hanover