MSD Coil Ballast Resistor Needed?

[scarceller]

Even with coil specs in hand I always bench test a coil for dwell times and across various system voltages. Here's a video of a crude bench test setup I use from time to time, it gives you a good idea of how a coils optimal dwell time can be found on a bench:
https://www.youtube.com/watch?v=a7dFdIdsZeU
Often I've found that coil specs are off and the actual saturation time differs on the bench than the time calculated mathematically. The very best test is the bench test.

What you need to do with the MSD coil is test it the same way I tested the 964 coil dwell and compare the results. Worth noting, the 964 coils are the same as the 3.2L coil.

The 3.2L (and 964) coil dwell times are as follows:

12vdc - 5ms
14vdc - 4ms
16vdc - 3ms
20vdc - 2ms

I suspect the MSD coil results will have longer dwell times.
The best way to know is to bench test a coil.

As seen system voltage impacts dwell time considerably, at 14v you can no longer fully charge the coil above 5000RPMs but at 12v this drops to 4000RPMs, just a 2volt system voltage drop effects the coil optimal dwell considerably! And at 16v your good till 6600RPMs

[wwest]

Originally Posted by scarceller

Even with coil specs in hand I always bench test a coil for dwell times and across various system voltages. Here's a video of a crude bench test setup I use from time to time, it gives you a good idea of how a coils optimal dwell time can be found on a bench:
https://www.youtube.com/watch?v=a7dFdIdsZeU
Often I've found that coil specs are off and the actual saturation time differs on the bench than the time calculated mathematically. The very best test is the bench test.

What you need to do with the MSD coil is test it the same way I tested the 964 coil dwell and compare the results. Worth noting, the 964 coils are the same as the 3.2L coil.

The 3.2L (and 964) coil dwell times are as follows:

12vdc - 5ms
14vdc - 4ms
16vdc - 3ms
20vdc - 2ms

I suspect the MSD coil results will have longer dwell times.
The best way to know is to bench test a coil.

As seen system voltage impacts dwell time considerably, at 14v you can no longer fully charge the coil above 5000RPMs but at 12v this drops to 4000RPMs, just a 2volt system voltage drop effects the coil optimal dwell considerably! And at 16v your good till 6600RPMs

"..I suspect the MSD coil results will have longer dwell times..."

Higher inductance value = REQUIRES longer dwell times to reach a specific charge level.

The worse conditions for firing the spark plug is at WOT, lower RPM range, and a HIGH engine load, RAPID acceleration. So not fully charging a coil at maximum engine RPM is not necessarily a design flaw.

[wwest]

Originally Posted by rick-l

I think I see a problem with your transformer

And that is..???

[scarceller]

Originally Posted by wwest

"..I suspect the MSD coil results will have longer dwell times..."

Higher inductance value = REQUIRES longer dwell times to reach a specific charge level.

The worse conditions for firing the spark plug is at WOT, lower RPM range, and a HIGH engine load, RAPID acceleration. So not fully charging a coil at maximum engine RPM is not necessarily a design flaw.

But peak cyl pressures in our 3.2L cars happen at WOT 5400-6000RPMs (peak torque) and even the stock design is a compromise here if the system voltage is below 15v. Putting in a coil that needs more time to dwell is a bad idea as it makes this problem worse.

I won't argue if a coil should be fully charged or not but I will say that the stock setup fully charges the coil so long as time permits. That's what the engineers designed in the 84-89 DME. I do agree that some other EFI system play with dwell times to reduce charge for low cyl pressure conditions but the 3.2L does not do this.

[scarceller]

This is an excellent source for dwell and testing for optimal dwell time:
Ignition Coil Dwell Calibration
You really need to bench test, don't trust a published mH number!

Even after bench testing you need to double check with coil in car because the DME (or EFI system) could limit current somewhat from what you tested on the bench. The in car conditions and the in car electronics can cause some differences. In the perfect setup you'd do in car testing but it's difficult (not impossible) to vary system voltage in car with engine running.

[wwest]

Originally Posted by scarceller

But peak cyl pressures in our 3.2L cars happen at WOT 5400-6000RPMs (peak torque) and even the stock design is a compromise here if the system voltage is below 15v.

I'm fairly sure that the peak cylinder pressure "rolls off" with/as RPM rises above mid-point. Peak torque can be more the result of plug firings/second, not cylinder charge level.

Putting in a coil that needs more time to dwell is a bad idea as it makes this problem worse.

Agreed, absolutely!


I won't argue if a coil should be fully charged or not but I will say that the stock setup fully charges the coil so long as time permits.

Again, yes, absolutely! "as long as time permits..."

That's what the engineers designed in the 84-89 DME. I do agree that some other EFI system play with dwell times to reduce charge for low cyl pressure conditions but the 3.2L does not do this.

Consider how little % the coil charge level changes beyond 3 time constants.

You strove for coil saturation for determining full charge, how much does that differ from the 5 time constants it takes to reach a full charge, or not?

[mysocal911]

Originally Posted by scarceller

I suspect the MSD coil results will have longer dwell times.

Will require longer dwell times!

The DME ECU doesn't know what ignition coil is being used and as such it uses its predetermined
dwell time based on the battery voltage and an assumed coil inductance. If the ECU were
actually monitoring the coil current (driver current), then the ECU could adjust the dwell
time based on a desired current.

Remember:

I (dwell current) = T (ECU dwell time) X V (battery voltage) / L (inductance - unknown for a non-stock coil)

So since the ECU doesn't know the inductance, the actual dwell current is unknown.

[scarceller]

My comment "I suspect the MSD coil results will have longer dwell times." was referring to bench test results to find optimal dwell time, I was not referring to in car dwell times.

But 100% agree that the actual in car dwell time will not change since it's baked into the DME via a dwell map. I've created new maps for different coils over the years, my advice is stick with the stock coil, it's fine for the naturally aspirated 3.2L the engineers did know what they where doing

Originally Posted by mysocal911

The DME ECU doesn't know what ignition coil is being used and as such it uses its predetermined
dwell time based on the battery voltage and an assumed coil inductance. If the ECU were
actually monitoring the coil current (driver current), then the ECU could adjust the dwell
time based on a desired current.

Remember:

I (dwell current) = T (ECU dwell time) X V (battery voltage) / L (inductance - unknown for a non-stock coil)

So since the ECU doesn't know the inductance, the actual dwell current is unknown.

[rick-l]

Originally Posted by wwest

And that is..???

this

Originally Posted by wwest

the magnetic field builds "slowly" in accordance with inductive reactance... The secondary voltage then rises in synchronization(?) with the rising magnetic field.

voltage appears on the secondary immediately.

[wwest]

Originally Posted by rick-l

this
voltage appears on the secondary immediately.

In the context of a transformer being used to convey energy from the primary winding to the secondary winding the rising magnetic field must "cut", pass through, the secondary winding in order for the secondary voltage to rise in accordance with primary voltage applied.

The more input inductance the transformer has the more the secondary voltage will lag the primary's applied voltage.

ELI the ICE man.....

Speaking here of TRANSFORMER action, not inductive ignition coil action.

[mysocal911]

Originally Posted by scarceller

My comment "I suspect the MSD coil results will have longer dwell times." was referring to bench test results to find optimal dwell time, I was not referring to in car dwell times.

But 100% agree that the actual in car dwell time will not change since it's baked into the DME via a dwell map. I've created new maps for different coils over the years, my advice is stick with the stock coil, it's fine for the naturally aspirated 3.2L the engineers did know what they where doing

Right on!

[dicklague]

Sal

Way off topic, but I watched your video on RhodeMap RI......scary stuff.

As a former Rhode Islander I am very interested......good analysis on your part.

Dick

[rick-l]

Originally Posted by wwest

In the context of a transformer being used to convey energy from the primary winding to the secondary winding the rising magnetic field must "cut", pass through, the secondary winding in order for the secondary voltage to rise in accordance with primary voltage applied.

The more input inductance the transformer has the more the secondary voltage will lag the primary's applied voltage.

ELI the ICE man.....

Speaking here of TRANSFORMER action, not inductive ignition coil action.

So the transformer equation does not apply to your transformer.
Look at Faraday's law for both windings (load on the secondary) and note the shared total flux appears in both equations and can be eliminated (the dt part). I think that is how you derive the transformer equation.

Input inductance is another of those standard terms in a transformer model. Is this leakage inductance, magnetization inductance, maybe all of the above?

If you apply a Sine wave to the primary with an unloaded secondary the input current will lag the voltage (90 deg) but with a load the real part dominates and the phase shift of the current goes to zero.

[scarceller]

Dick,

Yes, these HUD initiatives are scary stuff and most community leaders don't grasp the threats they pose to our way of life in America. Single family homes are looking to be wiped off the map if HUD has it's way. Rest assured, if not stopped it will creep into every community in America. It's eye opening to read what HUD writes, they are very clear on what they have in mind.

Thanks for watching.

Originally Posted by dicklague

Sal

Way off topic, but I watched your video on RhodeMap RI......scary stuff.

As a former Rhode Islander I am very interested......good analysis on your part.

Dick

[wwest]

Originally Posted by rick-l

So the transformer equation does not apply to your transformer.
Look at Faraday's law for both windings (load on the secondary) and note the shared total flux appears in both equations and can be eliminated (the dt part). I think that is how you derive the transformer equation.

Input inductance is another of those standard terms in a transformer model. Is this leakage inductance, magnetization inductance, maybe all of the above?

If you apply a Sine wave to the primary with an unloaded secondary the input current will lag the voltage (90 deg) but with a load the real part dominates and the phase shift of the current goes to zero.

If the sine wave frequency is low enough relative to the transformer's overall inductance the "lag", phase shift, will be minuscule, loaded or no.

But "here" what is of interest is the transformer reaction to the application of voltage with a SHARP leading edge, FAST rise time.

[rick-l]

Originally Posted by wwest

But "here" what is of interest is the transformer reaction to the application of voltage with a SHARP leading edge, FAST rise time.

Which is exactly what you get.... FLUX IN FLUX OUT.
The sine wave is to give an idea of what the magnetization inductance does. Perhaps you should read up on this a little.

[Pstallo]

I'm going to be honest. I'm not electrical enough to understand the last 25 or so posts (I still test a 9-volt battery by touching it to my tongue).

In short, I've been cruising around town with the MSD coil for the past few days and it never feels hot or anything. Do you think I need to replace it with a Bosch coil to prevent permanent damage?

[wwest]

Originally Posted by Pstallo

I'm going to be honest. I'm not electrical enough to understand the last 25 or so posts (I still test a 9-volt battery by touching it to my tongue).

In short, I've been cruising around town with the MSD coil for the past few days and it never feels hot or anything. Do you think I need to replace it with a Bosch coil to prevent permanent damage?

YES...!!

At high RPM the MSD coil will not be as fully charged as the OEM coil.

[scarceller]

Originally Posted by wwest

YES...!!

At high RPM the MSD coil will not be as fully charged as the OEM coil.

Agree, find a good used old black coil from a 3.2L or a 964. The new ones are now silver and made in Brazil, quality of the new coils is not as good as the older black coils.

[Sunroof]

.....You are right about the silver Brazilian made coils in that two failed in my 1973.5T. I had a hard time finding any suitable replacement until a few folks mentioned the MSD Blaster coil, which I bought. Now I am experiencing intermittent "sudden shut down" that may be attributable to that coil that may be contributing heat to the CDI unit. Please correct me if I wrong here...................the CDI unit was recently rebuilt, I use a 6500 limiting rotor, standard points and this MSD Blaster coil. After a long ride, the car shuts down!!!! After a long cool down it runs again. Wrong coil? rotor?. I just ordered the original black replacement (not the silver one) from a shop in Arizona, so I hope that helps. Other have stressed to use a "non-resistor rotor".

Bob