"Hot" Coil - Worth it?

[Greg Armstrong]

I've been planning to get a new coil, cap, rotor, and plug wires for a while now. I've looked at the "hot" coils with higher voltage... Are they worth it or should I just stick with a stock coil? I've heard high suppression wires are needed with a hot coil, true? I have a pertronix ignition, are there benefits with either type of coil when used with electronic ignition? Thanks for any insights.

[Larry B]

http://shop.pertronix.com/pertronix-406 ... kceJma3PMJ

the pertronix 40611 is the coil you want.

[wrink3]

I've used the Pertronix ignition and the above linked coil for several years. The 184 starts and runs great and the ignition is pretty much trouble free except for new plugs every couple of years (which were probably OK when I changed them). I doubt if it is "worth it" but if changing the ignition I'd change it all and if changing the coil I'd go with something from the ignition manufacturer who is familiar with the characteristics of the system. I opened the plug gap to .035 and that works well with the coil.
The higher voltage coil helps to light/burn a less than ideal air/fuel mixture--the auto manufacturers went there to for better ignition when using less fuel for economy and to help the emission controls. If you get your mixture burning with the lower voltage coil and smaller spark gap you're OK, no one checks the EPA fuel economy or emissions on most 184s or Cubs.

[Landreo]

The are several types of Pertronix systems. I have the basic ignitor and use a standard coil with copper wires. The voltage is determined by the spark plug gap not the potential coil voltage. A premium coil may be able to produce more current out the secondary but unless the coil core is physically larger then I doubt there is really much difference in the output current. If your old coil works then why get a new one? If you do go for the "hotter" coil you will not gain an advantage unless you widen the plug gap. For higher compression and higher speed engines, there may be an advantage to a larger gap but I suspect there is no real advantage in a low compression slow speed cub engine. On the other hand, having the "hotter" coil is not going to hurt anything.

[Larry B]

Will you see a difference using the Pertronix coil over a stock coil while running the tractor? No if your current coil is working properly.

The hardest thing the ignition system does is start the engine and the colder it is the harder it is. Running a warmed up tractor is the easiest thing it does. Assume your 184 is running and charging voltage is 13.5V with a standard 3 ohm coil 13.5V / 3 ohm = 4.5 Amps 13.5V X 4.5 A = 60.75 Watts
At running voltage the ignition system has about 61 watts of power available to the coil. More than enough to run most any engine. My 1967 Chevy with a 396 with 11:1 compression ratio ran just fine on an ignition like this. Now consider starting the tractor. When you start the engine you have the high current load of the starter pulling down the battery voltage which also lowers the voltage to the coil. Say the voltage drops to 9 volts. 9V / 3 ohm = 3 Amps 9V X 3A = 27 Watts While the engine is cranking you have about half the power available to the coil that you had with the engine running. Will 27 Watts start an engine with the rest of the ignition system in good condition? Yes. Now consider things like condition of wires, rotor to contact gap, plug gap, plug condition. As Landreo said plug gap is one of the factors determining how much voltage is required to jump the plug gap. Wider the gap the more voltage required, the problem arises when at starting the battery voltage goes low enough that the coil can't generate enough voltage to jump the gap.

Not all coils are created equal. An ignition coil is a transformer and there are many factors that affect the efficiency of a transformer. Number of windings, quality of wire, type of core metal, amount of core metal. So one coil may produce a certain amount of energy at a certain voltage while another will produce more or less energy at the same voltage. I have compared a couple Pertronix coils to less expensive import coils and there was a considerable difference. Ignition coils are limited to the amount of power that is applied to them and if you raise the output voltage you lower the output current. Ohm's law, there is no free lunch. In a 12 volt Battery/point/coil ignition system you are limited to somewhere around 75 Watts. More than that and you start cooking points and wiring. This limits the voltage out of the coil to around 20,000 to 40,000 volts depending on voltage applied. you can make a coil that produces 60,000 volts on 60 Watts but the current would be too low. Totally unneeded anyway for a C60 engine. Where you will see a difference with a high quality "hot" coils is with cold starting, not running.

There is a way to get more energy to the plugs when starting is to use a 1.5 ohm coil and a 1.5 ohm ballast resistor that is bypassed during starting. So now you have that 9 volts to a 1.5 ohm coil. 9V / 1.5 ohm = 6 Amps 9V X 6A = 54 Watts. You now have 54 Watts available to the coil during starting instead of 27 watts if the voltage drops to 9 volts. When you release the key the ballast resistor is not bypassed and the system operates on 3 ohms. This conversion can be done with a 1.5 ohm coil and 1.5 ohm ballast resistor a standard lawnmower starter relay without needing to do any wiring under the dash panel.

[Greg Armstrong]

Very detailed! I'm a broadcast radio engineer and very familiar with electrical concepts of primary to secondary ratios and power remaining constant. Higher voltage jumps gaps, so lower current on the secondary doesn't produce an issue since the arc is what ignites the fuel. It seems that the above linked coil should be sufficient, especially since I've seen other posts referencing many "stock" import coils failing prematurely. My coil is original and I've had issues with longer cranking to start, probably because the new plugs I put in last year are partially fouled, probably because the coil is getting weak. ...so I want to replace it all.

What about wires? Does the 40KV coil need high suppression, or are standard copper good enough? For what it's worth, I'm using NGK AB6 plugs.

[Larry B]

Either type plug wire will work. Suppression wires were invented to stop the broadband RF interference when cars got AM radios. The solid core wires acted as broadcast antenna. The solution was nonmetallic carbon core suppression wires. Nowadays we have internal resistor spark plugs that will also suppress the RF emissions. Pertronix recommends suppression wires to possibly avoid interference problems with their electronic ignition modules. I have installed them using both solid core and suppression wires with no problems. Supression wires do introduce some resistance to the system but not enough to make a difference except in very low battery voltage conditions. The NGK AB-6 is a non resistor plug so I would recommend a high quality carbon core suppression set of wires since you have the Pertronix ignition.
Back in the day when a tachometer was expensive some mechanics kept a solid core wire around and would install it on one of the plugs in the car and turn on the AM radio and listen for the speed of the ticking sound and could set idle RPM from that.

[Greg Armstrong]

Thanks Larry, that makes perfect sense. Doubt there is a set of "cub" carbon core wires out there... Probably have to custom make them. I appreciate all of the help and info!

[Larry B]

These should work
http://www.tractorpartsasap.com/Spark-P ... mAQAvD_BwE

Also, you said you run the NGK AB-6 spark plug. Unless you are running the tractor hot and hard that might be a colder plug than you need. That converts to about a 10 heat range on the Champion scale and The minimum for a 184 Champion plug would be a D15 or D15Y which is still fairly cold. I used to run D18Y plugs for heavy mowing but since the 184 got retired from mowing I run D21 plugs. If you are fouling plugs you might try a hotter heat range plug.

[Gary Dotson]

On the subject of spark plug wires, metallic vs. suppression core, you can have the best of both. Over the years, several manufacturers have offered spiral core wires, including Pertronix. These wires have a conventional suppression core, with a very fine, stainless steel wire wrap. They have a very low ohm value but still suppress very well. I doubt that Pertronix offers a kit specifically for the Cub, but would have semi-tailored kits for earlier 4 cyl engines. I have used these on the last couple early Corvettes I've done and had plenty excess wire left over to do two of my Cubs. It's nice stuff!

[Greg Armstrong]

Larry, I will certainly try the D18Y. I was under the impression the NGK AB6 was closer to 16... Guess I was wrong! When I got the tractor it had a D16, D21, and 2 Autolite plugs. AKA whatever the P.O. had lying around.

Thanks for the wire suggestions Gary. Is there a cost effective crimp tool out there? I hate spending a ton for a tool I'll use once in a blue moon.

[Larry B]

https://www.ebay.com/itm/Wire-Stripper- ... 0033.m2042

the above tool is an example of a crimp tool that would work. You would use the position closest to the handles. You can probably get a crimp tool at a local auto parts store. I would never recommend a plier type crimp tool for crimping insulated terminals but plug wires don't need that kind of pressure so a plier type will work.

[Gary Dotson]

Taylor wire has a nice crimping tool #43390 (Belden clone) for less than $20. I found it on E-bay for $17 and change, with free ship. I also did a little digging on the Pertronix wire set and found #704190 for Cub type of applications. I found the wires at Summit Racing but should be available from any Pertronix dealer.

[BigBill]

Hotter coils we use in high rpm engines. As the rpms go up the output of the coil lowers.

If you want a hotter spark for starting the older 12v ignition cars ran a wire from the solinoid smaller threaded stud. That reads 12v when the engine is cranking. Run the wire from the solinoid to the coil. This gives a hotter spark when starting.

[Greg Armstrong]

Shopping list has been made! Can't wait to get everything on and hopefully see some improvement. I'll probably change the plugs really soon though, sounds like the cold AB6 plugs are probably fouled and new plugs will probably go a long way until I can get everything else done.