MSD 6AL-2 for twinplug application

1100sport · 10-07-2016, 08:47 AM

Hi everyone,
I currently have a MSD 6AL-2 programmable fitted to my 930 - with locked distributor, and I am very happy with it.
I am considering twinplugging my engine and would like to know if I can use One module of MSD 6AL-2 to drive 2 coils in parallel (and still rely on the programmable curve). I know the power sent to the coils will be halved but I am fine with that. I just want to know if it is feasible or not. I know a lot of people who have done the same thing with the old MSD 6AL and were pretty happy...
Thanks in advance for your help!
Mathieu

JohnJL · 10-07-2016, 11:18 AM

Search here, several thorough threads.

1100sport · 10-07-2016, 12:54 PM

Thanks John - I did search extensively but did not find an thread where an MSD 6AL-2 has been used in a twin plug configuration. If you can point me to one or even better enlighten me regarding my query, I'd be very grateful!
Mathieu

Jonny H · 10-07-2016, 02:21 PM

It may 'appear' to work but the spark output will be greatly reduced so will be a compromise at best.

Before committing to a big expenditure on a twin spark setup, you might try a true multi spark unit like our CDI+ (MSD is just a single spark > 3400 RPM) with your current setup.

We will have dyno data end of October which will test our dual spark unit against a 'proper' twin plug setup.

wayner · 10-07-2016, 02:29 PM

I went the opposite way. I bought a pair of the non programable 6al2 models that are less expensive, and an adjustable JB distributor

JohnJL · 10-07-2016, 02:50 PM

Search on my name, there are threads on 2 of my cars concerning this. The short of it is you want 2 msd boxes, one for the top plugs and another for the bottom. One of my card is exactly like wayner describes with the JB dizzy.

Fred Winterburn · 10-07-2016, 07:06 PM

Mathieu,
This was from a few months back when I ran a test in the thread titled MSD firing two coils simultaneously. Fred

MSD 6A firing two coils simultaneously.
Folks,
There was a thread I read here from a few years ago titled 'MSD ignition exposed'. In that thread at least one member was firing a twin plug engine with a single MSD ignition box. I did a quick test today and I certainly do not recommend doing this. It works, but not very well, and that is provided the coils are in parallel with the MSD output and not in series. In series the impedance is doubled and the energy output from both coils is so low that it isn't worth considering. Here are the test results. By the way, some of you may be surprised at how low the voltage output is with MSD given the advertising. The unit I tested was a 2009 model MSD 6A. It is basically the same design that they used in the 1970s. The output is completely dependent on battery voltage as it does not use an oscillator type power supply to charge the discharge capacitor. Instead, the emitters of two power transistors in parallel, are connected directly to the battery by the thick red wire. When triggered 'on', the transistors attempt to charge the 1uF discharge capacitor in one half cycle through a massive transformer (at least that's how the circuit appears to operate) The spark duration is short too (about 35 to 40 uS) and much shorter than you would expect for a 1uF capacitor which should give a spark duration of at least 100uS with most CDis. The time between individual sparks is almost exactly 1mS, which I think is far too long after the first spark to be of any use (my opinion).
Results of quick test using two more or less matched coils.
1500rpm (6cyl)
-Maximum voltage at calibrated spark gap 28kV with single coil (4 sparks separated by 1mS).
-Maximum voltage attainable at calibrated spark gap 20kV with two coils in parallel. Still able to produce 4 sparks.
2000rpm (6cyl):
-Maximum voltage at calibrated spark gap 28kV with single coil (3 sparks separated by 1mS)
-Maximum voltage attainable at calibrated spark gap 20kV with two coils in parallel. Still able to produce 3 sparks.
4000rpm (6cyl):
Maximum voltage at calibrated spark gap 26kV with single coil (2 sparks separated by 1mS).
Maximum voltage attainable at calibrated spark gap 19kV with two coils in parallel. Still able to produce 2 sparks.
6000 rpm (6cyl):
Maximum voltage at calibrated spark gap 24kV with single coil. ( 1 spark)
Maximum voltage attainable at calibrated spark gap 16kV with two coils in parallel. Single spark.
The above testing was done at 12.5V applied. Charging voltage near 14V would make the values higher. What I didn't check for, but perhaps will do another time, is check how much shorter the spark duration is with two sparks plugs firing at once. Certainly the energy of each spark is considerably lower than if the MSD 6A were driving a single coil. One thing that did stand out on the scope was the massive voltage overshoot in comparison to the actual attainable gap breakdown voltage when two coils are used. So despite the lower energy, the spark plug wires and coil secondary windings are still taking a beating from voltage stress with the CD output split between two coils. Fred

1100sport · 10-09-2016, 12:40 PM

Thanks a lot! Seems like a bad idea. The thing is, I've come to really appreciate the ability to "map" the curve. However, I have not seen this feature ever used when 2 cdi are put to service in a dual plug application. In such case, it seems like there is no alternative but to rely on mechanical advance (with a twin plug distributor).
I guess it may be possible to set both modules identically, and let each module drive its coil. But I would be a bit concerned that they don't work perfectly in synch.
I am keen to keep a distributor, as I like the old school look. If anyone has an idea, I would be eager to learn it. Thanks again!

Jonny H · 12:31 AM

Quote:

Originally Posted by 1100sport

Thanks a lot! Seems like a bad idea. The thing is, I've come to really appreciate the ability to "map" the curve. However, I have not seen this feature ever used when 2 cdi are put to service in a dual plug application. In such case, it seems like there is no alternative but to rely on mechanical advance (with a twin plug distributor).
I guess it may be possible to set both modules identically, and let each module drive its coil. But I would be a bit concerned that they don't work perfectly in synch.
I am keen to keep a distributor, as I like the old school look. If anyone has an idea, I would be eager to learn it. Thanks again!

Have a read our CDI+ manual. It will give you near twin plug performance from one unit. Fully mappable, soft and hard limiters etc.

We are just working on a firmware release that will allow you to run two of our units, one synching from the other on a standard twin plug distributor. First unit has the map and the second synchs from the first.

Here's a link:

CDI+ Info