What coil to use

[alexiskai]

If you’re comparing oil to oil, an oil filled Flamethrower coil performed identically to a UC14 coil on my test bench. Can’t speak to longevity. Both would need to be operated terminals-up.

 

[The Master Cylinder]

Regarding orientation, if the coil is "filled" with oil(is there an air gap? How much? How much of the windings would not be in oil?) upside down or right side up shouldn't matter? What if it's laying on it's side?

From Pertronix, maker of the Flame Thrower coil;

Warning: Do not mount oil-filled ignition coils upside down or horizontally. Proper vertical installation, with the terminal facing upward, is essential to ensure optimal performance and prevent oil leakage or internal damage. Incorrect mounting may lead to reduced coil efficiency, misfires, or premature failure. For non-vertical mounting applications, use an epoxy-filled coil designed to handle such orientations. Always follow the manufacturer’s guidelines for safe and reliable operation.

 

[2speed]

I have a TO35 Massey Ferguson tractor that takes a UC14 coil. It is mounted horizontally. It's been on there for over 40 years. The same with a Kohler 301 lawn tractor. The coil is mounted horizontally. Aren't some ford Y-blocks mounted horizontally?


They're all oil filled.

 

[katy]

[QUOTE[]Aren't some ford Y-blocks mounted horizontally?[/QUOTE]

I've seen lots of these Ford coils mounted horizontally, in fact I have one that I keep for a spare for my A.

 

[ursus]

As I recall, you're converting a car from 12V to 6V, is that right? Many 12V coils will work on a 6V system as well. You can check with an ammeter:

1. Connect one terminal of the coil to a 6V battery. Ideally you want to match + to + or - to -, but if your coil has confusing labels like BATT and DIST then just hook it up, doesn't matter.
2. Connect the other terminal of the coil to an ammeter and then connect the ammeter to the other terminal of the battery, completing the circuit.
3. The battery should begin to discharge through the coil.
4. If your ammeter shows about 3A or more, the coil should work fine on a 6V car.

I have a coil here marked "12V" that draws 3.5A when cold and 2.8A when hot. Works fine on 6V, nice spark.

I find that the number of amps a coil draws is often a good indicator of its strength. My best 6V coils draw 5.3A.

Isn't the series of connections described here already available in a Model A ignition system? If the points are closed and the ignition is switched on would we see the same kind of result on the ammeter?

 

[2speed]

You do, that's the jiggle when you crank the engine. I would assume that he's using a much more accurate and precise ammeter to get the readings.

 

[40 Deluxe]

The 6 volt coil that some of the vendors have are around $20.00. The flame thrower coil is around $60.00. Is it a better coil or just a higher price. It is 1.5 ohms.

Keep in mind that any coil only puts out enough voltage to jump the spark plug gap. If 5,000 volts is enough to fire the plug, that is all the coil will produce. No matter if it is a Super Duper 50,000 Volt Flame Throwing Monster, it will only produce 5,000 volts.
Now, if the plug gap is worn, or set too wide, or wires are bad, or you have a high compression head, the voltage will go up but not to the 50,000 volt level.

 

[rotorwrench]

Perhaps the needs of aircraft coils are different, but I don't think this is an accurate depiction of Model A coil design. These coils don't need to be insulated. They need to have waste heat – created by the resistance within the circuit – conducted away from the windings. Oil is better at doing that than epoxy.

An oil-filled coil mounted terminals-up will have a long service life and give a spark equal to or better than your average epoxy coil. The original terminals-down orientation worked because of the tar potting material, but there's nothing intrinsically better about it.

An ignition coil is an inductor. Induction coils in basic electricity are used to step voltage up or down. They only function on AC current or pulsating DC which is like half wave AC. The breaker points provide the half wave pulsating DC. Most ignition coils are designed to step up system voltage to a high enough tension voltage so it will jump the gap of a spark plug with the aid of a capacitor to keep the points from burning up and prolong the discharge as long as possible. The insulation in the coil pack keeps the high tension voltage from discharging anywhere else internally during the induction cycle.

Magneto ignition is used in aircraft engines so they have a big magnet that provides the magnetic field so they aren't connected to any power source. They have a smaller coil that's in an insulated pack to prevent flash over.

An ignition coil is full of resistance type wire so they just make them in different resistance levels depending on the vehicles system voltage. If the coil needs protection such as the early V8 coils, they add a ballast resistor to the circuit. The model A can type coil could take around 7-volts with no ballast. On the little Mallory type coils in the early V8s through 1948, they used about a 0.8 Ohm ballast. The 6-volt systems after 1948, like the model A, didn't need a ballast with a 1.5-Ohm primary. The 1956 models with the new 12-volt system, tried to use a 1.5-Ohm coil but it didn't work out so they added a ballast of around 1.3 to 1.5-Ohms. They kept this design till the electronic ignition systems came out. The 3-Ohm coil has been around about as long as electronic ignition systems. They use modern materials that can take the heat of a 12-volt system without using a ballast.

A coil should be able to work in any mounting configuration. The problem is cheap replacement parts that just don't cut it. If a coil runs so hot that you can't touch it then something is wrong with it. If it leaks then it isn't properly sealed. I remember a lot of old late 50s & 60s Fords with the old mustard top coils mounted horizontally. I had a 64 T-Bird with one like that. I had to convert it back to a standard points system after the transistorized ignition's transistor gave out. That old mustard top worked just fine after that.

 

[nkaminar]

40 Deluxe, Another way that the voltage required to jump the gap in the plug will go up is with air under compression. Higher compression requires more voltage. The old spark plug testers has a way to test them under pressure.

 

[40 Deluxe]

40 Deluxe, Another way that the voltage required to jump the gap in the plug will go up is with air under compression. Higher compression requires more voltage. The old spark plug testers has a way to test them under pressure.

Agreed, which is why I mentioned a high compression head. Those old testers had 2 spark plug ports and an air pressure regulator. In one port you installed a brand new plug with the correct gap. In the other port you installed the customer's used plug and switched on the tester's coil (which was deliberately weak). Spark was sent to both plugs. You gradually increased air pressure and noted when the spark blew out (could not jump the gap). The customer's plug would quit first, and you could raise the pressure on the new plug and show the customer how weak his old plugs were.

 

[katy]

Keep in mind that any coil only puts out enough voltage to jump the spark plug gap. If 5,000 volts is enough to fire the plug, that is all the coil will produce. No matter if it is a Super Duper 50,000 Volt Flame Throwing Monster, it will only produce 5,000 volts.

I suspect that the voltage may not be higher but the amperage could be higher giving a hotter spark.

 

[rotorwrench]

The amount of high tension voltage output of any ignition coil depends on the turn ratio between the primary coil and the secondary coil. Most coils were designed to put out around 20 k volts. It can vary a lot depending on the design amount of turns in the fine wire secondary. The capacitance level of the condenser also varies depending on the coil design.

The modern high energy coil packs used with current designs have a lot of advantages over the old designs in that they only have to fire one time in the two crankshaft revolutions. This translates to longer dwell times for complete magnetic saturation of the primary coil. The electronic pulse generation will last way longer than the breaker points. They put out a far hotter high tension voltage as well.

Scheduled maintenance on aircraft plugs requires a thorough clean, adjust, and test every 100 hours. I tested them for 60 seconds at 120 psi. If they won't deliver a consistent spark pulse for that time and pressure then it is time for a new plug. At $100 a piece, a person doesn't take the test lightly. With two magneto sets, it's easy to test for rpm drop during preflight run up. We can't do that in our automobiles but new plugs are a lot less expensive too.