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BTW - I didn't compare the systems to the PerTronix versions. So, although I don't have access to corporate secrets and schematics, nor have I used an oscilloscope to prove each one, I would say that based on their characteristics:

  • The P-I is fixed dwell without current limiting (like points) and therefore uses a coil resistor.
  • The P-II appears to use fixed dwell with current-limiting like the GM 4-pin, and therefore no coil resistor.
  • The P-III appears to use calculating power for true dwell control, and uses some of that calculating power to also incorporate multi-spark, and determine RPM for rev-limiting. It therefore uses no coil resistor. However, due to it's ability to somewhat adapt to other coils than the one recommended, I believe it also uses current-limiting. Or, it's a lot smarter than we give it credit for.
I don't tinker with distributors much anymore, and most of the stuff I play with is distributorless with multiple coils and full dwell control. However, if working on a distributor car that's stock or mild, and power or hair-splitting economy were not required, I'd probably just use a P-I or similar conversion. It just has to run. Much wilder than that, I'd probably go straight to the P-III or equivalent and lots of sharp tuning for all the benefits of the whole enchilada.


David
 

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Think of the coil like a bucket, and the water flowing into it is from a faucet.
Dang, PSIG. That is GOOD.

I've been reading up on ignitions for years, and this is the best Pertronix thread i've ever seen. Seriously- this should be a sticky.
 

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I agree and think it should go in a different area of the site. Maybe re-title "before you install a Pertronix read this" or something to that effect cause there may be other people in other areas of this site that don't follow the Galaxie pages and have installed it incorrectly due to just following the instructions.
 

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BTW - I didn't compare the systems to the PerTronix versions. So, although I don't have access to corporate secrets and schematics, nor have I used an oscilloscope to prove each one, I would say that based on their characteristics:

  • The P-I is fixed dwell without current limiting (like points) and therefore uses a coil resistor.
  • The P-II appears to use fixed dwell with current-limiting like the GM 4-pin, and therefore no coil resistor.
  • The P-III appears to use calculating power for true dwell control, and uses some of that calculating power to also incorporate multi-spark, and determine RPM for rev-limiting. It therefore uses no coil resistor. However, due to it's ability to somewhat adapt to other coils than the one recommended, I believe it also uses current-limiting. Or, it's a lot smarter than we give it credit for.
I don't tinker with distributors much anymore, and most of the stuff I play with is distributorless with multiple coils and full dwell control. However, if working on a distributor car that's stock or mild, and power or hair-splitting economy were not required, I'd probably just use a P-I or similar conversion. It just has to run. Much wilder than that, I'd probably go straight to the P-III or equivalent and lots of sharp tuning for all the benefits of the whole enchilada.


David

That's what I'm talking about Pert I no control just a steady dwell.

Pert II I'd like to know the secret but your Explanation like the GM module makes sense although I've not seen one in person.

I knew all about the bucket of water analogy, it's the DWELL control that I didn't believe, and still can't fully accept without a deeper look at the electronics of a Pert II system.

I don't use the II or III system because I don't race...
 

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Actually, dwell control is a fairly simple process, and a child's digital watch has the power to do the calculations, though it may not have the speed at $9.99. Let's break-down the process:
  • Coil ON time
  • Firing time
  • Wait time
We have had electronic tachometers for 50 years, and it's simple to calculate. The module sees the RPM, and therefore knows how long it has at the current RPM to accomplish the 3 steps above. Using a V8 at 1000 RPM, time between firings is .015 seconds or 15 milliseconds (15ms). Let's say your coil needs 4ms to fully saturate, and it takes 1ms for the spark to fully fire (spark burn). So:
  • Coil ON = 4ms
  • Firing time = 1ms
  • Wait time = 10ms
So, the module just uses the stopwatch function of your kid's watch to wait 1ms + 10ms before turning power to the coil on for the next firing for 4ms. There's your 15ms. Bingo - perfectly controlled dwell.

Here's the rub. At 3000 RPM, there is just 5ms between firings, and just barely enough time to get full power out of the coil with no wait time. Any RPM above that will give a weaker spark. To get it to spark to redline, we close the spark plug gap to .035" so the weak spark can still fire at that RPM. It still runs, but the power is down slightly from the small .035 gap and weak remaining spark.

Because we have dwell control, we can remove the resistor from the coil power feed. Now the coil will saturate in 3ms, and we can get full spark to 4500 and a stronger one than we had at redline. We might be able to open the plug gap to .045".

Want more? Then we switch to a coil that will saturate even faster, like an HEI/TFI coil. Now we can get not only full spark power at redline, but we can open the gap still further to get a much larger spark for more efficient mixture ignition with more power and efficiency. With the hot spark and faster burn, we may even be able to reduce the WOT timing advance a bit, further increasing our power output. And the arms race goes on and on...

David
 

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I just installed the pII and 45k coil .6 ohm. I called tech support and they say to put full voltage to the coil and module.

The pII has variable dwell I confirmed this with a meter at 1000 rpm dwell is 10 at 2500 rpm it goes up around 25. It will also shut down if the ignition switch sticks on. The pI won't do that I have that on my 64 Galaxie and works fine but I dint trust the mustangs ignition switch so I went with the PII.

This thing works great took out any miss my 70 Mach1 had runs smooth.
 

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I think what everybody is saying is if you have a stock coil leave it alone. If you have an aftermarket coil change the wiring, (for pertronix I) is this correct??
 
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