The Stovebolt Site Forums The Shop Area The Electrical Bay Using 12 volt coil in 6 volt ignition?

Hi. To provide a better voltage spark at the plugs can a 12 volt coil (no ballast resister) be substituted for the stock 6 volt coil?

Anyone tried using platinum plugs to provide better performance (than the stock J8's)?

I wouldn't suggest changing any electrical components from one voltage to another. If you add the 12volt coil it could possibly damage your ignition circuit.

Ign. points can only stand so much curent (amps). If you do anything to increase the flow you are going to burn the points. If you want more spark get an electronic ign. changeover with the matching coil.

A 12 volt coil has higher primary resistance than a 6V. If it works at all, you'll get very low secondary voltage, and the engine will run really lousy!
Jerry

Your 12 volt coil will work if it doesn't have an internal ballast resistor. For standard, contact ignition systems, all ignition coils have approximately the same primary resistance, about 1.5 ohms, plus or minus a couple of tenths. Secondary resistance varies by manufacturer preference, but is not a factor with your coil as long as it is a Delco-Remy, or a replacement with the OEM specifications. High performance coils, heavy duty coils and those made for various electronic ignition systems vary in primary and secondary resistance, depending on the manufacturer and the ignition system. Some electronic systems even use the 'standard' coil- that is, nothing special, except a label.

I don't see where you should have any trouble with the 12-volt coil in your 6-volt system, as long as the 12-volt coil has about 1.5 ohms of primary resistance and secondary resistance in the range of 9000-10000 ohms; some variation is alright.

Harvester

The internal balast resistor is only used on the primary side to regulate current it does change the current in the secondary by cutting it in half. The ignition coil itself is a basic step up tranformer. These transformers work off a turn to turn ratio. So let's say we need 20,000 volts on the secondary going to the engine. In order to find the turns ratio we would divide 20,000 by 6(volts). This calculates to 1(primary) to 3,333(secondary) turns of wire. Now if we had a 12 system we would need the same 20,000 volts. This coil would need to be coil 1(primary) to 1,166(secondary) since this is 20,000/12. So your 6 volt system requiring 20,000 would be 6v/20,000=amps of the secondary/4amps primary. You would end up with .0012 amps and 20,000 volts. If we use the 12 volt coil with the 6 volt system. Now, we would have 6 volts multiplied by 1,166 from the 12 volt secondary. This would equal 9,996 volts. Your current will also change. To find the current :6v/9,996=amps sec/4amps primary. By the way amps is found by dividing 6v by the resistance 1.5 ohms. The secondary current would be .0024 amps compared to the original .0012. So just as wrench bender stated your current would double. Hot rod Lincoln was on the right track with your voltage being thrown off which is now 9,996 volts. The gap of your spark plugs depends on this high voltage to jump the gap. These numbers aren't exact. I just used 20,000 as an example. I hope this is some what clear.

Actually, the magnetic induction capability of a coil is rated in "ampere-turns". Very low resistance coil primary windings flow lots of current and produce high secondary voltage, but that happens at the expense of very short point life. A set of conventional contact points can carry about 5 amps and survive for 10,000 miles or so at normal highway speeds. The big Mallory SuperCoil we used back in the 60's on the drag strip with their corresponding dual-point centrifugal advance only distributor used to be the hot setup. The condenser used with that system was about the diameter of a quarter, and about 2 inches tall. It had to be mounted on the outside of the distributor- - - -no room under the cap! Points were good for about one weekend at the drag strip, and the hotrodders were lined up at Dad's shop door on Monday so their daily driver/weekend racer could get them back and forth to work all week!
Jerry

That sounds like some fun weekends back in the 60's. Were you at the age to enjoy that? You are correct about the phrase rated in ampere-turns, but I just used turn ratio to simplify it. So your ampere turns might be 80 to 400. Your turns ratio would be 1:5. So your voltage would be the primary 1 to secondary 5. Now, your current would be the primary 5 to secondary 1.

A plain old 12 volt coil still only runs on about 6-8 volts. That's what the resistor (external or internal) is for, to drop the voltage to lower the amps through the points so they survive.

Check out an old Motor's Repair Manual, they have a pretty good write up on ignition systems. Quoting from a 1963 truck one:
The ignition coils used with 12-volt systems are specially designed 6-volt coils which operate with a resistor....

I was taught that a 12 volt (external resistor) coil was just the same as a 6 volt; interchangeable.. Seems that's not entirely true according to the motors manual, but not that far off either.

Grigg

I was campaigning a 47 Ford coupe occasionally in the drag racing stock classes back in the early 60's when I was in high school, but the primary racing effort at the family shop was a few years earlier, with a 34 Ford 3-window coupe on the local 1/4 mile dirt tracks. Dad built some of the hottest round track engines in Middle Tennessee, running them on alcohol and Hydrogen Peroxide. His basic relationship with the drag racers was taking lots of their money while making their ignition systems and automatic transmissions survive all the abuse they dished out.
Jerry

I understand at normal running conditions that the ignition coil is around 6-8 volts because of the external balast resistors in series with the igntion coil. The only problem I see would be on start up. When the engine is started the external balast resistor is bypassed by the ignition switch; therefore, the igiontion coil on 12volt system will have 12volts on start up. A coil that would step 12v and 6v would be different secondary windings. Your 6v coil is going to need more turns of copper in the secondary then the 12v coil to obtain the same voltage. Hence the reason why a 6v coil is 8-10 bucks more because you are paying for more copper.