What coil to use
- Thread starter oldford
- Start date
Synchro909
Well-known member
IMO, a flame thrower coil is NOT worth 3 times an ordinary one.
Hint - turn the coil over so that the terminals are facing up. I'm sure Henry put them up the other way to save a few inches of wire but modern coils don't like being @$$ up. I was told that by a guy who has forgotten more about model As than I'll ever know after I had the third coil fail (including a flame thrower). No failures since.
Hint - turn the coil over so that the terminals are facing up. I'm sure Henry put them up the other way to save a few inches of wire but modern coils don't like being @$$ up. I was told that by a guy who has forgotten more about model As than I'll ever know after I had the third coil fail (including a flame thrower). No failures since.
The Master Cylinder
Well-known member
I have never had a flame thrower fail. Ensure you get the epoxy fill Flame Thrower and it works fine the way Henry had it. Oil filled coils don't like being pointed down.
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alexiskai
Well-known member
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.
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.
rotorwrench
Well-known member
The old Ford coils used what can best be described as tar for the internal insulation. Generally, the only time that the tar will melt is if the ignition switch was inadvertently left on and the breaker points happened to be closed. They will overheat if that happens. In normal use the breaker is always moving so the coil doesn't get very hot. It was likely sometime after WWII when they started using a liquid insulation and some of that stuff was poisonous. Epoxy came into wider use in the later 60s and is still the best insulator. Cheap coils may still have a liquid insulation. It pays to check on that in the manufacturers information if they have any.
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alexiskai
Well-known member
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.
alexiskai
Well-known member
I measure strength of the spark after 5 minutes of heat saturation on a Snap-On MT-640 coil tester.
The amp draw of the coil needs to be balanced with the life of the points. Higher amps, shorter life of the points. That's why in 12 volt systems a resistor is needed. More volts, means more amps pushed through.
A 6 volt coil is 1.5ohms. 12V are 3.0 ohms. Certain 12V coils have an internal resistor, they are usually marked as such, and then don't need the external ballast resistor.
A Standard Ignition UC14 6 volt coil is oil filled. The Flamethrowers seem to be e
epoxy.
Hotter sparks are usually associated with high compression engines, as the voltage needs to be higher to make the spark jump on the high compression. At 4:1 not much of an issue for a Model A.
A 6 volt coil is 1.5ohms. 12V are 3.0 ohms. Certain 12V coils have an internal resistor, they are usually marked as such, and then don't need the external ballast resistor.
A Standard Ignition UC14 6 volt coil is oil filled. The Flamethrowers seem to be e
epoxy.
Hotter sparks are usually associated with high compression engines, as the voltage needs to be higher to make the spark jump on the high compression. At 4:1 not much of an issue for a Model A.
Have had terrible experience with oil filled (cheapo) coils which most if not all are made outside the US. The oil filled coils shouldn't be used with terminals down which doesn't provide cooling for windings as stated above. Stay with the epoxy or find used tar filled coils that can be tested.
alexiskai
Well-known member
Yeah, I should note that I am building a mild street rod with 6.5:1 compression and a different distributor. I also have condensers with a range of capacitances, so I can tune my circuit by matching, e.g., a 5.3A coil with a .36 µF condenser.
Couple of corrections to your statements above:
- Not all 12V coils are 3Ω, I have one here that's 1.7Ω. The 3Ω coils are the ones with the internal resistor.
– Pertronix makes both oil and epoxy Flamethrower coils.
Many folks are associating oil-filled coils with poor quality and that is simply not true. What you're actually seeing is that 90% of all coils are oil-filled, both good and bad. I've seen failed oil coils and failed epoxy coils. You should not judge a coil simply by what's in it.
54Hotrodder
Junior Member
I've purchased my OEM replacement from Snyder's and it does fine.
Ok, a 12V ignition circuit should have around 3 ohms in it, to limit amps to the points. Coil+Resistor or Coil w/internal resistor.
Points should have around 4 amps through them to get a decent life.
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?