Correct internal or external coil for pertronix points eliminater

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Plymouth Duster

Plymouth Duster

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Hey guys
I’ve always had points minus a few hei cars. But this is my first Slant and while tuning her up and changing fluids, adjustment etc noticed she had a pertronix points eliminater kit. Since I’m doing cap, rotor, wires, plugs, fluids and already did a carb rebuild as she sat for years what’s the correct coil for this ignition setup? Still has a ballast resistor and if anyone has a economy or OEM part number for a stock or maybe a higher voltage budget minded coil please let me know. Like to change it for peace of mind. It’s a 225 slant post 74 drool tube motor I believe 77 225
Thanks as always
JR
 
It all depends on what Pertronix says as to which coil to use. I would go on their site and see what it says about the slant 6 kit. Or call them.
 
RustyRatRod said:
what Pertronix says as to which coil to use
Click to expand...
The ohms for the coils differ per application. Pertronix will show a range from .06 to 3.0 for their I II III conversions.
If I remember for 4 and 6 cylinder engines a 3.0 ohm coil is used.Chrysler electronic ignition uses a 1.5 ohm coil.
The Pertronix I uses the ballast the II and III it is by-passed and the correct coil for them is listed.
Most Likely you will have the common I kit. The stock Chrysler 1.5 ohm will work fine.
 
If Pertronix I doesn't control coil current, then a resistor is needed to control coil current.
For an ECU era chrysler the resistor is 0.5 Ohms, and should be used with a factory coil.
Points cars had resistors in the .6-.8 ohm range, and again use with factory coil.

Higher turn ratios and other coil mods are of no advantage and arguably a detriment in this application.
They can be useful at high rpm, high load where dwell time limited.
Higher voltage is mostly marketing phewey.
The voltage required to jump the spark gap depends on the cobustion chamber conditions and the gap distance. The fact that a coil may be able to produce a higher voltage would only help if there is a problem initiating spark. Maybe more important in general driving is the ability to continue to provide spark energy long enough to develop a nice kernal of flame. After that, the flame development is going grow on its own.
 
Darter6 said:
The ohms for the coils differ per application. Pertronix will show a range from .06 to 3.0 for their I II III conversions.
If I remember for 4 and 6 cylinder engines a 3.0 ohm coil is used.Chrysler electronic ignition uses a 1.5 ohm coil.
The Pertronix I uses the ballast the II and III it is by-passed and the correct coil for them is listed.
Most Likely you will have the common I kit. The stock Chrysler 1.5 ohm will work fine.
Click to expand...
 
Yea looks like a factory old coil and the job was def old as I had to replace the rotor shield with magnets and green tape. Had a dead cylinder and couldn’t figure it out. When I pull apart the found the one missing magnet on the rotor shield

DB68779C-BF6E-430B-B576-C30B675303BA.jpeg
 
Plymouth Duster said:
Thanks r

Rusty. I have part number will check site now. If not call them tomorrow
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I think this is safest, since the coil is really what dictates whether you run a resistor. I would just call them to see what they say. We can say this and that all day, but you want it RIGHT, I am sure.
 
I don't know why the heck "these companies" don't actually TEST a few popular combinations, as that is the type of thing on which they will be used
 
Pertronix puts out such BS, I do not know how they get away with it. And why people buy their junk. While looking at their website for info, I noticed they claim the Pert I ignitor doubles the voltage. If the same coil is used the voltage stays the same.
 
Bewy said:
Pertronix puts out such BS, I do not know how they get away with it. And why people buy their junk. While looking at their website for info, I noticed they claim the Pert I ignitor doubles the voltage. If the same coil is used the voltage stays the same.
Click to expand...

The voltage does not strictly depend on the coil. The formula for the coil voltage is V = L x di/dt.
The voltage is equal to the inductance of the coil times the speed of the current change. So the voltage output of the coil theoretically can depend of how fast the current is switched off. This can be faster with an electronic ignition. The inductance & turns ratio of the coil also figure into the calculation.

The above is an extremely simplified explanation of how things work. The coil and the ECU can both have an effect on spark voltage. However there are a lot of other factors. In reality, the gap size of the spark plug limits the high voltage in operation. When the spark plug breaks down, the high voltage goes away.

The moral to the story is that car ignitions are designed as a “system” and using them as designed will likely give you the best results.

When manufacturers advertise specs for their parts, they generally describe the conditions that are most favorable for their parts. This is usually a theoretical or “best case” situation which may not be practical in real life. So if they are comparing the highest possible voltage that can be generated by their ignition to a car with worn out points, they may not be lying, but they are not really telling the truth.
 
RustyRatRod said:
I think this is safest, since the coil is really what dictates whether you run a resistor. I would just call them to see what they say. We can say this and that all day, but you want it RIGHT, I am sure.
Click to expand...
Agreed 100%. I try not to half *** anything. I’m actually driving myself nuts now to find a correct size and appearing door ((outer) handle button latch screw that was apparent missing hence why my door handle button and lift mechanism feel off.

one of my hack friends goes “yea jjst throw a bigger self tapper in there I just cringed, lol. Maybe ur cars but I can’t fathom do that so have had no door handle for 5 days now.

I believe the screw is a 10-32 or 10-24. It pretty sure 10-32 and Approximately 1/4-1/2” and I am leaning towards 1/2”. If any one replaced there handles and has one driver side or at least the latch screw please let me know
Pic attached

658B94BC-BFC5-4890-8EB6-8CD49ED1A13B.jpeg
 
Mike69cuda said:
The voltage does not strictly depend on the coil. The formula for the coil voltage is V = L x di/dt.
The voltage is equal to the inductance of the coil times the speed of the current change. So the voltage output of the coil theoretically can depend of how fast the current is switched off. This can be faster with an electronic ignition. The inductance & turns ratio of the coil also figure into the calculation.

The above is an extremely simplified explanation of how things work. The coil and the ECU can both have an effect on spark voltage. However there are a lot of other factors. In reality, the gap size of the spark plug limits the high voltage in operation. When the spark plug breaks down, the high voltage goes away.

The moral to the story is that car ignitions are designed as a “system” and using them as designed will likely give you the best results.

When manufacturers advertise specs for their parts, they generally describe the conditions that are most favorable for their parts. This is usually a theoretical or “best case” situation which may not be practical in real life. So if they are comparing the highest possible voltage that can be generated by their ignition to a car with worn out points, they may not be lying, but they are not really telling the truth.
Click to expand...
Agreed!!!
Fortunately I’ve never used one or purchased one and have only used points and I think a few hei in later 70s 80s type gm cars. So this was a mystery to me when I did the tune, heck I didn’t know what it was till I noticed and the dead Cylinder and what a debacle that was, took me to a while to figure out that the magnet fell off the rotor magnet cover.

tested wires and plugs with ohm meter and switched two rotors and caps and was ready to buy a reman dizzy with points when I noticed a magnet missing and bam problem solved. I think it’s wired pos neg to coil and pos still going to ballast so OEM setup, but other then ease of cleaning and or adjusting points I see $120 dollars well spent in other areas. I would definitely not buy this setup as points have been good to me in 25+ years of working on Oldsmobiles/GMs and Mopars

AAD71BBF-6301-4891-ABB4-F37F1E38037C.jpeg
 
Mike 69,
The voltage mentioned in post #11 refers to the secondary voltage. As best as I can recall, Pert did not differentiate between pri & sec voltage in their quote, but they meant sec voltage because the suckers fall for the big numbers [ 60,000v is better than 30,000 v, right ].
The sec voltage is governed by pri voltage & turns ratio. Since this kit does not change the pri voltage to any noticeable amount, there will be no increase in sec voltage. That was my point.
 
Just had another look at the Pert site. Says 'delivers twice the voltage to the spark plugs'.

Another dubious claim is that their high end module that fits INSIDE the dist & multi sparks right through the rpm range. This would be a huge selling feature if true & one would expect the competition to pull one apart & copy it; hasn't happened that I am aware of. My understanding is that only CD ign can multi spark to high rpms on an 8 cyl engine; this system requires a large capacitor & transformer & would not fit inside said module.
 
What you say it partially true, but is not the whole story. If it was only the primary voltage and the turns ratio, you would only get a secondary voltage of about 12000 volts (12 volts times a 100:1 turns ratio). The primary voltage of interest is created by the collapsing magnetic field, not the 12V supply. Google flyback transformer operation.

The primary voltage on a points system is basically a function of the speed of changing the current in the transformer (assuming the same coil). See the formula I posted above.

An electronic system is basically the same, except the voltage is also limited by a snubber out the output transistor. For example if the primary voltage is limited to 500 volts, the 500 volts times 100:1 turns ratio is 50,00 volts.

About 100:1 is standard turns ratio for a car coil, I think some of the high performance models may have about 115:1.
 
Mike,
Well aware of the collapsing field in the pri side generating about 200-250v, & it is this that multiplies with the turns ratio.

It seems that coil makers have gradually woken up to the fact that it is the heat [ the heating affect of DC current ] that ignites the A/F mixture, not the voltage; the voltage is merely the enabler of current flow. Many E core have lower TRs than the 'performance' coils of yester year that were often over 100:1. The 1" spark looks great on the gadget at the speed shop, & 60,000v is waaaay more impressive than 0.1 amp, so guess which one gets the sale, lol.
These are the TRs of just a few ind ign coils that I have specs on: Crane PS91 54:1. Crane LX-9
 
..oops, pushed the wrong key. Crane LX-91 57:1, Accel 140009 70:1, Accel 380876 85:1, MSD 8207 70:1, MSD HEI coil 70:1.

The sec voltage used to ionise the plug gap is usually [ & should be ] well below the available sec coil voltage, what is left is reserve voltage. CT magazine did a comprehensive test years ago on coils/ign. Even when plug gap was increased to 060, the reqd sec voltage did not increase from 28kv that a smaller gap reqd. This will vary.
 
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