Pertronix coil and ignition system

[zimmy]

planning on getting a Pertronix ignition...
do i need to get the Pertronix coil also?....ziimmmy

 

[Trevor Jessie]

I did not. I used a ballasted coil from autozone that they listed for my car.

 

[Keoke]

Hi Zimmy, While it is not mandatory to use a Pertronix or Lucas Sport Coil the best overall performance will be attained if you use one or the other of these uprated coils.---Fwiw---Keoke

 

[Trevor Jessie]

Why will it give you better performance?

 

[JakSeMasTTU]

Based on my understanding of the Pertronix Ignition controller, using the Pertronix coil in conjunction with the controller would not be mandatory. I assume however, that the Pertronix Engineers would try to "optimize" the ignition controller for the specifications of their own proprietary coil. Each coil will pass itself off as "hi-voltage" (Lucas or aftermarket), but to me that is just clever marketing. Each coil will have slightly different specifications. Therefore if you graphed Output Voltage vs. Engine RPMs, I'm willing to bet (although I don't have the hi-voltage bench set-up to test this), that no coil would be truly higher voltage (than OEM) from start to finish. They would each have their "weaknesses" based on hysteresis, DC resistance, Ferro-fluid heat dissipation, etc. What the Pertronix ignition controller does, is allows for more consistent spark voltage through the entire engine operating range. It does this by using a microcontroller with Transistorized outputs; instead of the make-break mechanical switching of a traditional points set-up. Traditional points ignition uses a ballast resistor to limit current (of course capacitor charge/discharge time is also considered) and thereby heat. If you are using an aftermarket ignition controller, I would strongly recommend removing the Ballast resistor (we did on my Uncle's MG). Although you will affect the timing, this can be adjusted easily enough with a turn of the distributor to compensate (adjusting sparkplug gap may also be neccesary). Leaving the ballast resistor in place will limit the input voltage to the coil, thereby lmiting the output voltage to the Sparkplug. It won't make or break you, but every little bit helps, right? For reference, my Uncle uses the Mallory Electronic Distributor, the Pertronix Coil, & the Pertronix Second-Strike Controller. He's been using that for a year now, and it has worked great for him with no hiccups! His MG is his daily driver, no less. Back to the original question: Do you need to match brands on coil and ignition controllers? No. Would I recommend it? I guess so. Please correct me if I've overlooked a critical factor, or made an error somehow. Everythig I've said is based on "book knowledge" more than hands on experience.

 

[zimmy]

i have a 1275 , dont think i have a ballast resistor.....z

 

[Trevor Jessie]

Zimmy, you may not have a seperate ballast, but it may be internal to the coil.

Thanks for your thoughts Bryan, but now... how would I know if I'm not getting the needed output from for my plugs? They appear normal in color and undamaged. My power seems fine and there are no signs of a miss under load or high rpm cruise.

 

[JakSeMasTTU]

First question: I'm no MG expert (My Uncle has an MG, I have a Miata), but I would assume that resistor wire is more likely than a component ballast resistor in the OEM MG set-up. Measure the resistance of the wire going from ignition to coil. I would expect about .5 ohm or so. If so, bypass this wire when you install Ignition controller. Ammendment: I now remember! (it's been a year ago, I've slept since then). In the OEM set-up on his '69 MG midget, the .5 Ohm ballast was located in the Ammeter style Tach in his dash. So if you go with the aftermarket Ignition controller, make sure you don't have the Ammeter style Tach. If you drive a later model MG, I have been told that those have modern Pulse Sensing Tachs (dklawson wrote a quality article on retro-fitting ammeter style to pulse-sensing). Therefore, I would expect those later model MG/AH to use resistor wire from Ignition switch to coil, or a component ballast resistor.

Second Question: Well proof is in the pudding, I always say. If it's working to your satisfaction, don't worry about it. To properly compare performance with/without ballast resistor, I would make an instrument measurement. I personally do not have an O-scope with high voltage Set-up that you would need (20-30KV is lots!). Therefore I can only speak academically, but theoretically there would be less voltage available at the sparkplug with the ballast resistor. In all fairness, it may be splitting hairs. we could of course calculate this sort of thing mathematically, but I'd rather not. An automotive ignition coil is very close cousin to a transformer. So if you are familiar with AC voltage transformers, it follows many of the same principles (higher voltage in, higher voltage out). Perhaps someone else who has closely compared this set-up could chime in? My background is RF, not automotive electronics.

 

[JerryB]

"""""""do i need to get the Pertronix coil also?....""""""

not unless you want to contribute to the economy ....OR ...if you need a coil with internal ballast or your now coil has NOT the proper internal resistance.

Pertronix recommends "their coil" as there is a very nice profit margin in coils.....even more than the modules. Any good OIL FILLED coil, with the correct internal resistance and mounted properly will suffice for a street type motor.

Disconnect the wire to the + terminal of the coil, and with the key on, mesure the voltage. IF it's less than about 9 volts you have a resistance wire to the coil or a ballast resistor either built in the car or an external ballast resistor on the firewall or somewhere else in that circuit.

IF you have 12.5 volts at the + wire you need to have a coil that has about 2.5 to 3 ohms internal resistance. Measure with a digital ohmmeter between the + and - terminals on the coil. IF your coil measures less than 2 ohms internal resistance you need to add a ballast resistor.

To be more concise, when using the Pertronix module you want either ballast voltage or a coil with 3 ohms internal resistance so the voltage to the module is no more than 9 volts.

There has been a series of posts on this topic bout 3 weeks ago , and you can referr to them also.

If you are using a box such as the MSD 6A or the Crane equvalent you do not need ballast voltage and you can use a 1.5 ohm coil.

It does not take a lot of spark energy to fire a motor say under 9:1 compresion and at lower rpm's.