hi Henry , No , you have a very common misconception there . The reason you measure 8 or 9 V is the meter reads the average value over time of the volts . ( if a nice analog meter — ,a digital will read garbage as it samples V in time , about 3 / sec) Varying volts not read right
Much more complicated than that . When the points are open 12 v appears , there as no current in the ballast , no drop ,a full 12 shows up When the points close it drops in proportion to the resistance present ,reaching about 5 -6 A , or a bit more , indicating about a 1 ohm total ohms of ballast and coil . If using your .3 ohm coil , only 1.5 v on coil (!) 11.5 on ballast . .More typically coil is around 1 ohm , ballast 0, 6 so about 5 v . So the average value in time of 5 closed and 12 open is the 8 or 9 .
This is complicated by the ballast is iron wire made to go much higher in ohms if it gets hot , especially at idle , where you are measuring this
So why all this ? The coil has a time constant , a physical reality inherent to all coils around a few milliseconds, It s L ( mH ) divided R .( ohms) It takes a few time constants for core to “saturate” ,or fill with stored energy for the spark .So about 4 /1000 sec to fill up for full spark
note with the R “on bottom “ high R means faster saturation of core ( think if it as filling a bucket — takes time ( current flow) —-that is where the spark energy is stored. — saturated core happens after about two time constants , means a full bucket ( full magnetic field actually)
Counterintuitive to many that higher R makes it charge up faster —! BUT if we make R too big to get this aspect real fast , the total current once saturated is now made less . Compromise must be made
E ( spark) equals 1/2 L I squared . L is size of coil , note I squared .
Once saturated it is a linear DC circuit all you have is volts divided by ohms .
For any given setup , ( ohms total) raising the volts 10 % raises the final current 10 % . I = V divided by R ..
I is the cause of the magnetic field you get .
So if you lose 1 volt off 13 , you have 12 . Now, due to square , ratio of spark energy is now 144 to 169 . Physics and EE , done
Pertronix can cost you intensity at higher rpm , but they do have a way , later on Why drag racers use 16 v batteries , overcomes that . But ideas to linearly raise current ( low ohm coil ,has to be used then with no or low ballast , = not only burn up points ,the 5 A goes up , you just made the time constant potentially LONGER to get to the higher current.
The real problem in ignitions is there is not enough time to fill the coil up at over say 4k rpm , spark E starts dropping off . Only a few milliseconds between sparks at 6000 rpm , might be 1/2 the spark it was at 3000, — equals misfire
The time constant of a coil design does not change much ; larger coil means longer wire in the coil , L and R both go up . Other way too .both go down .
It is NOT a transformer ,( although does that too) it is an energy store device Thicker wire takes more room , for same turns , wire is forced to be longer ( R up ) etc
Once you have enough to light it there is no return on making more , or , say a huge coil at 10 amps same L/R
At idle there are many time constants per spark , current keeps on coming long after coil is full , coil will get too hot fast ( average current goes way up ) .. now — a brilliant thing — iron wire gets very hot in ballast ( why ceramic) R goes up with temp protects coil from melting at idle . And an R shortens time constant too at high rpm, iron is then cool , average time on is less Awwright
These are engineered systems, messing with them can hurt rather than help . Correct coil ohms and matching ballast are critical to the trade off . Mr Kettering knew ALL of this in 1920 . I mean , he just might have optimized the trades? laugh
And if not , 100 years have led to coil on plug , that fixes the time constant problem , plenty of time to fill bucket , 8 x as long, don't care about the 1 volt either - EZ!
Also why many V12 in 30’s have two 6 cyl setups
I actually have a patent on a way of using two coils on a v8 with one stock distributor , Same functional idea as very old designs with dual rotor ( not mine) were in the famous DuCoil distributors for flat heads in the 40’s ( 6 volt systems to fight too) Way to go !
7000 rom becomes 3500 to the coil . It was actually the same as two 4 cylinder ignitions, twice the time to fill up . All you need on a V8 .
Another way to fill up better is get more dwell , why mopar dual points , higher dwell is directly impacting higher rpm, more time to fill up . fussy yes , use dwell meter . Pertronix can get more dwell than points as solid state is fast ( HEI too) but after all that, the 1 volt thing is still there , but practically today the increased dwell of electronic does get a lot of the V loss back. Much Better than single point , big boon to GM guys
But this discussion is about whether mopar stock 300 is ok , and especially failure modes of “ improvements”
But end of day losing a volt in electronic switch hurts you no matter what you do , with a normal coil , as saturation current in a given coil WILL be lower by ratio of the net volts it gets . A squared impact on spark intensity .
Despite the love of chevy boys MSD is a waste of money .Coil still limits it Of course chevy boys do not have dual points or a hemi . An extra spark coming way late ( multiple spark discharge = msd) does nothing for you, way too late .. sad joke, great marketing story
Maybe they need to adapt 300F distributor to SBC ? 15-20 % more !
Real engineering means 300B and F went 140 with points, 6500 ok, Petty did ok with Daytona on points, 1234 finish . Garlits did ok with 50’s points . Nuff said
Magneto is the best , left out of this , but they have points too
They will do the job , will not fail with minor care , if they do , a 10 minute adjustment after 30 k miles? away you go . # 1 cause of point ignition trouble is junk chinese capacitors sold now , change that first .Even “burned “ points work ok . Bad cap gives very weak spark , intermittently too hope this helps , J On Nov 27, 2025, at 9:48 AM, henry.schleimer@xxxxxxxxxxxxxxx wrote:
Just on the power issue John raised, I would like to correct this often-repeated quote as the coil does not get 12V/13V with Chrysler ballast resistor circuits. More like 8V/9V while running. While the numbers are wrong, John is technically right that there is a proportional power loss. But he neglects the other side of the equation in that power is also inversely proportional to resistance. Lowering the coil resistance will increase the power to the coil, if that’s what you want. Back in my younger days, the go to hot up mod was to fit a Bosch GT40R coil. Didn’t matter whether you had a Ford, Holden or Chrysler, that red coil on the side of your engine showed you meant business! The primary resistance is 1.2 ohms which is typically lower than factory coils, therefore more power with a higher voltage output. I have had one on my Val with factory electronic ignition (pre ELB version) for 25 years now without any problem. About a year ago I bought one at my local parts store (in stock/on the shelf) for our 65 Mustang. Having an aftermarket part available for 40 years tells you all you need to know about reputation and reliability. Sadly, they now seem to be discontinued… Probably not enough need for this type of coil any more to justify room on the shelves. Cheers Henry From: chrysler-300-club-international@xxxxxxxxxxxxxxxx <chrysler-300-club-international@xxxxxxxxxxxxxxxx> On Behalf Of John Grady
Sent: Thursday, 27 November 2025 4:58 AM
To: Bob Jasinski <rpjasin@xxxxxxxxxxx>
Cc: Allan Zolis <allanzolis@xxxxxxxxx>; chrysler-300-club-international@xxxxxxxxxxxxxxxx
Subject: Re: {Chrysler 300} 1961 300 g tachometer question agree,in fact nothing wrong with points,10k miles no bs ,curve in MSD will not match stock. Trouble with pertronics if it punts you walk. Maybe a long wolk. Points and business card you go.Points do not lose the 1 volt of solid state either. Power in EE goes as square of volts,you lose 144/169 , significantly weaker spark --
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