...yet another Pertronix thread!

[xray]

So I'm finishing up some final sorting out of minor issues (major ones have been fixed finally) and was looking over the info from Pertronix against what has been posted here as well as in my files. The Flamethrower coil I have is the recommended one from Pertronix with 3ohms of resistance in the primary coil. The stock 240Z coil is 1.5 ohms.

The Pertronix instructions say to bypass the ballast resistor. Fine. But, pics shown here, as well as the diagram from ZHome (and supplied here) show the Pertronix attached (I think) diagrammed in parallel to the BR in the run circuit. Is it safe to assume the author of that diagram was implying use of the stock coil? If so, is my modifed diagram below correct for "bypassing" the ballast resistor when using the 3ohm Flamethrower?

An aftermarket seller of Pertronix devices states that using a coil with improper resistance has been known to cause problems in the ignition system, and mirrors info from Pertronix that 6-cyl cars should use a 3-ohm resistance coil:

http://www.vintageperformance.com/retrorockets/avoiding_problems.htm

My reason for asking is a slight misfire at 4500-5000rpm which I think may be related to a weak spark (since my other problems were derived from the same issue.) Since the Pertronix is designed to see the full 12V in the run and start circuit...If the BR is still in the run circuit with an internally resisted coil, the output would be weaker than intended, correct?

Any electrical gurus (ZsonDaBrain, EScanlon others--I'm looking your way!) with advice would be helpful.

Pic 1: wiring in the engine bay (courtesy BambiKiller 240--RIP)

Pic 2: Pertronix diagram

Pic 3: modified diagram, for use with 3ohm Flamethrower

Thanks for the help,

Steve

[Nissanman]

Essentially, yes, your modified diag. shorting out or bypassing the ballast resistor is correct for a coil which does NOT require an external resistor.

Note that the tacho. will also get the full voltage.

What the implications are with that, I'm not sure:ermm:

Having a ballast resistor in the circuit with a 3ohm coil will severely limit the primary current at high revs, when point dwell time is decreasing.

As a temporary fix, simply bridge the resistor out or shift the wire from one end of the resistor and double it up with the wire on its' other end.

Drive the car and see if your misfire has gone.

Running a superfluous BR is not as bad as omitting one when it is necessary.

Has been known to cause coils to EXPLODE:finger:

[xray]

Thanks, Nissanman...

I thought the tach always got 12V, and the point (pun intended) of the ballast resistor was to protect the points from seeing too much voltage and burning out. Then again, an electrical guru I am not.

[Nissanman]

The idea of the ballast resistor is interesting.

When you attempt to start the engine, everything at that point could be at its' most troublesome.

Battery could be cold and low, engine could be cold and oil very hard to move around, etc.

The START position applies full battery voltage to the ignition system to give the engine its' best chance of firing up.

Notice I didn't say 12V:surprised

The battery could be a lot less than the nominal 12V.

Anyhoo, presuming the engine cranks over and fires, the return of the key to the RUN position switches the BR into circuit so the coil power supply is limited.

As you have already measured, the coil is only 1.5ohm and if left to run on what would now be ~13.6V, nominal float voltage for a 12V lead acid battery, it would soon get tired and eventually, very angry:mad:

Ignition points are protected by the condenser [capacitor] that is connected from the hot terminal to the distributor body, thus earth.

This device will absorb the voltage spikes generated when the points open and protect the contacts from arcing and therefore burning.

[The primary ignition circuit is very inductive and the back EMF generated when the points open is huge.]

It also stores this electrical energy and gives it back to the primary circuit the next time the points close.

If you want to experiment, try running the engine without an effective condenser.

It will fart and cough usually, due to a weaker spark being generated.

It will also generate a huge arc when the points open, so don't run it without the condenser for long.

[xray]

Bump for more advice....anyone?

Thanks,

Steve

[gnosez]

I'm running the pertonix in my euro dizzy coupled w/MSD-6a box, the 3.0ohm coil, BS-7 NGK plugs, 8mm Magnacore wires, and no BR. Runs just fine.

[xray]

I got some more info from Pertronix, and with a quick confirmatory call to their tech support line, confirmed my notion in the first post.

If you're running the 3ohm Flamethrower coil, the red wire goes to the (+) terminal on the coil. Jump the ballast resistor, connecting the B/W and G/W wires. With its internal resistance, the 3ohm FT coil does not generate the needed voltage for optimal spark if the ballast resistor is left in the run circuit.

But, if you're using a stock 1.5ohm coil, the picture depicting the red wire from the Pertronix connecting to the 12v+ side of the BR is correct. As stated on the Pertronix website, running a low resistance coil alone can cause premature failure of the Ignitor.

Here's the .pdf below:

After altering the wiring, I took the Z out for a spin. It revved to redline without a complaint. Punched it and it didn't sputter or lose power. Looks like the vast majority of mechanical gremlins are worked out!

...Now for the little things.:stupid:

Steve

ignitor12vneg.pdf

[mlc240z]

Thanks guys.

guess i'm wired wrong:tapemouth. i'll have to hit the garage tonight to correct it.

any info/guess on what full current/full time will do to the tach? i'd hate to get correct resistance to save a $70 ignitor and fry a $$$$ original tach.

[Nissanman]

If the tacho. is of the IMPULSE type then it shouldn't matter if the BR is removed.

An impulse tacho. as the name implies, reads engine RPM by the number of impulses it receives on the primary ignition wire.

The input is a simple wire loop that passes through a small transformer core at the rear of the instrument.

If it works OK with the Pertronix conversion then it should continue to work OK without the BR.

[xray]

In all my searching (obviously not exhaustive) here and other automotive forums you're the only person so far that brings up the need for a BR to protect the tachometer. Not that I doubt you,but could you explain that in greater detail for those of us in the dark? Here I am thinking it was only for the coil/points etc.

Thanks,

Steve

[Nissanman]

You are correct, the BR is primarily there to protect the 1.5ohm coil from meltdown when the engine is running.

It was just something I noticed in the wiring diagram, removing the BR applied full voltage to both the coil and the tacho.

As I mentioned above, for an impulse tacho. it may not matter at all.