Ignition coil/ballast resistor

[l-wood 240z]

I have a 1972 240z with a L28 engine swap. When it was done the shop left some of the 240 parts on the 280 engine, distributor, dual stand-up carbs and the coil. I have a spare 280 that I am trying to swap some parts off of, here is my question. The ballast resistor that is necessary for the coil to work properly is wired up differently from 72 to 77. If I take the coil from the 280 to try and match up with my 240, how exactly do I wire in the resistor. Stock 240 resistor only has one wire coming out, stock 280 resistor has two wires and is wired in differently. Can you tell me how to properly wire in the resistor.

[Jehannum]

1. The ballast resistor is there to protect the points in your distributor.

2. The 280's coil is wired up differently because its ignition is transistorized (no points in the distributor).

You can get away with using the stock 240 ignition wiring, if you've got the 240 distributor on the L28, but it's probably better in the long run if you swap to either the 280Z's ignition (a big box under the dash), or the 280ZX's ignition (swapping to the 280ZX distributor and E12-80 unit).

So, the bottom line is that without either the 280Z's distributor and transistor unit or the 240Z's distributor and points, your L28 isn't going to run at all.

Decide which way you want to go, and it'll be easier to decide what to do with the ballast resistor - with the transistorized ignition, the resistor is pointless (except for keeping the tach somewhat closer to true).

[bpilati]

I believe that there is also a relationship between the ballast resistor and the tachometer.

[Jehannum]

I believe that there is also a relationship between the ballast resistor and the tachometer.

Yeah, it reads about 400RPM higher without the resistor. At least, mine does.

[Nissanman]

The ballast resistor is there to protect the points in your distributor.

Just to clarify the function of a ballast resistor.

This device is switched OUT when the key is in the START position. That allows the ignition coil to be connected to full battery voltage to enable starting the engine.

Then it is switched IN when the key is returned to ON position after the engine fires up. That allows the ignition coil to be connected to a reduced battery voltage for running the engine.

This type of coil must not be used without the correct use of the ballast resistor.

If it is connected to full battery voltage all the time it will burn out.

The protection of the ignition points is achieved by the use of the points condenser.

This device, technically an electrical capacitor, absorbs the back EMF generated when the points open.

[The primary coil circuit that the points energise, is highly inductive and interrupting an inductive circuit will generate very high voltages due to the collapse of the magnetic flux in the associated circuit.]

Without an effective capacitor, there will be horrendous sparking of the opening points and they will quickly burn out.

Of course there are ignition coils which are designed to operate without a ballast resistor [with points] and ignition coils designed to be used with transistorised ignition systems [without points].

These are two different devices as well and must not be confused.

A points coil used on a transistorised ignition is a bomb waiting to go off:finger:

[Jehannum]

Running a hot coil without the ballast resistor on a points distributor resulted in significantly shorter life of the points that with the stock coil, hence my "protect the points" comment.

[sblake01]

The ballast resistor's job is to keep from cooking the coil, not the points. The voltage crossing the points is only to trigger the coil to discharge. High tension coil voltage only runs down the wires through the dist cap and rotor. Semantics. Running any coil without the ballast resistor on a points distrubutor will shorten the life of the points. As far as 'hot' coils go, the ignition will only use the voltage it needs and a given speed, load, etc. If you have a 40000, 60000, 100000 volt coil, it's just overkill.

[Jehannum]

The ballast resistor's job is to keep from cooking the coil, not the points. The voltage crossing the points is only to trigger the coil to discharge. High tension coil voltage only runs down the wires through the dist cap and rotor. Semantics. Running any coil without the ballast resistor on a points distrubutor will shorten the life of the points. As far as 'hot' coils go, the ignition will only use the voltage it needs and a given speed, load, etc. If you have a 40000, 60000, 100000 volt coil, it's just overkill.

You can run a bigger gap with a hotter coil. It's a good supporting modification for when you intend higher cylinder pressures, either via cam or forced induction.

Stock on stock, though, you're right.

[sblake01]

Stock or modified, I'm right. If you just want the have the last word on this, go ahead, it really doesn't matter to me.