Pertronix/CDI users - what about this mod?

Modded Rotor

Steve,

I think you'll find that the issue is really high resistance of either the ignition wires or plugs that causes the issue described by the article.

With a high resistance and the least path of resistance the spark will tend to go back to the distributer and to ground. That's what causes the blown rotor. Cheap knock -off parts and not doing the normal checks with a meter.

A CD box or high output coil only increases the spark and the resistance is even a greater problem.

I've seen the problem ( bosch rotor; cheap Braziailan or otherwise) but it always came down to wires and plugs. ( maybe a missing distributer ground) My rotors last several times longer than say a cap, plugs, or wires.

To answer your last question, there is resistance in any electrical device. The trick is to meter it and know when it's outside the norm and effecting the engine's performance.

61
 
Yes, but why do they add a resistor to the rotor if wires and "R" plugs have such? Seems like a mismatch in specs along the spark route. I am putting in new wires and W8DC's along with rotor and cap and seeing this mod got me thinking - just enough to get me in trouble as usual.

61porsche said:
there is resistance in any electrical device. The trick is to meter it and know when it's outside the norm and effecting the engine's performance.
Click to expand...
 
Stevehose said:
Anyone know if this rotor resistor mod would be of any benefit with the Pertronix or is it not high enough output to make a difference? Why is a resistor needed in the stock rotor - radio noise?

http://www.huelsmann.us/bugman/RotorTech.html
Click to expand...

Agree with the above. From anecdotal experience, point elimination/substitution on an otherwise stock/tame engine won't benefit from lowering rotor resistance.

The problem of rotor issues (overheating or meltdown) typically arises when you introduce a so-called "super/blaster coil" (e.g. Crane PS92 etc.) in combination with non resistance wires and non resistance terminals and non resistance plugs. Per G. Ohm and his maxim, the ignition system is designed to include a modicum of resistance. If the high tension leads do not resist some of the aftermarket coil's energy, the rotor may. Having tried a variety of aftermarket ignition hardware, the only stock Bosch rotor failures have been due to unexplained carbon button disintegration (at the top of the distributor cap) and normal wear. I have modified rotors out of sheer curiosity, but never noticed any difference.

Have pondered how the modification and potential weight change might affect balance of rotor and introduce a potential wear factor, but this never developed as a significant issue.

As to why the stock Bosch rotor is designed with resistance, I can only hazard an uneducated guess. The words "broad spectrum practicality" come to mind, and radio interference may have a lot to do with it. Consider also that the mass produced ignition system was designed to be used in many different applications (by many different manufacturers) and adding resistance may have been the lowest common denominator for lessening foreseen ignition-related issues. Another less-than-obvious factor might have been unit costs. Bosch may have perceived a greater demand for resistor rotors and that may have lessened their unit cost over non-resistor rotors. (Are Bosch non-resistor plugs as plentiful as they once were and are the non-resistor plugs always less expensive?) Consider that the power starved VW flat four was typically equipped with a resistor rotor (the point of your linked article). The intent was likely to minimize a wide range of potential issues, including radio interference. The same reasoning typically applies to recommended ignition timing. Advancing a bit usually optimizes output, but not necessarily for each and every unit produced. Ignoring this fact and playing with the odds may result in an otherwise avoidable (if not embarrassing) test of the manufacturer's warranty and . . . finances.
CRN-730-0092_AT.jpg
 
Long ago and far away

There were once cars without high end stereos, FI, etc. Those early rotors were solid up until the early sixties. Crossfiring through wires, etc. was prevelant. I remember the old trick of lifting the hood at night to check for arcing. Crude, but effective.

The resistor is simple- it reduces the current. My theory is that they just were into a new phase of engineering. I didn't say I agreed. Kinda like galvanizing sheetmetal; they didn't want to do it, they just went through the analytics and decided lawsuits were just too costly. And the part is cheaper with less brass/ copper.

With modern silicone wires, EPDM jackets, better plugs, wider gaps, the resistor isn't needed. But it sure helps sales! ( for Bosch).

I run headers, so I learned quickly that a stock set of wires fried pretty quick. So, I use 635 wires- silicone.

We drive old cars, lavish them with as much attention and money as ( sometimes) reasonable and sometimes not.( She who must be obeyed or writes the check for the AMX.)

I learned along time ago that driving something different could and would get me in trouble or worse ( Texas murphy's law) somewhere I shouldn't be at the time. I didn't stop me then and I'm too stubborn now.

So, I just go through my mental checklist, add a couple tools/ spares to the boot, and get on with it. That's the reality. Just have a little fun.
 
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