View Full Version : Triggering Dual Ignitions
07-08-2003, 09:22 AM
We are running a mag trigger distributor into a 8680 timing control feeding a 6AL on our road race car. I want to install a complete backup 6AL system including a second coil and a coil selector. Can I trigger both 6AL's simultaneuosly with the same signal from my 8680, or do I need to switch this signal along with the power to the units? We are using an 8911 tach splitter to take care of the tach.
07-09-2003, 07:20 PM
Are you running a dual pickup distributor?
MSD Tech 1
07-10-2003, 08:36 AM
No. It is an 85561 distributor triggering an 8680 timing control. We race long distances at widely varying altitudes and vary the total timing several degrees depending on the altitude. We are installing a redundant 6AL system this year, carrying the spare in the car rather than on the chase truck. Can I join the two white wires from the 6AL's together and drive them both with the yellow wire from the 8680? There is a drawing at the Martel Bros site that shows a points-style distributor running a dual ignition setup and they have the white wires joined. http://www.martelbros.com/msd/support/45.htm
Another question about the 8680 -
What is the start-up mode of the 8680 controller? Does it default to the maximum timing then retard after a few cycles? We installed another 8680 in another motor and it seems to have a lot of timing at the start. If this is the case, how many cycles does it take for the controller to decide how much to retard?
07-17-2003, 09:39 AM
A true dual ignition setup would require a dual pickup distributor, two timing controls, two MSD Ignition Controls, two MSD Coils, an Automatic Coil Selector and a MSD to MSD Change Over Switch. With this combination, if any component is in the system fails or is suspect you can switch over and be on a completely different setup.
If you run a single pickup and only one timing control then you risk the chance of shutting down both systems if either of those parts fail.
07-18-2003, 03:50 AM
In order to have complete redundancy I would need dual distributors and two plugs per cylinder. Since I only have two MSD6AL's, two coils, a coil selector and a switch I'll take a chance on the rest. Can you answer the questions I asked?
07-18-2003, 11:24 AM
You can trigger both units from one trigger source, but if one of the ignition units has a problem on the input circuit then the other unit will be affected as well. Also, if the timing control unit fails or the trigger pickup in the distributor fails then you will loose both systems at the same time. I feel that the additional parts and wiring will increase your risk of a problem and therefore will not provide you with the benefit you are looking for.
As for your second question, the PN 8680 will retard the timing the full amount during startup as long as the cranking speed of the engine is 300 rpm or more and the input voltage to the PN 8680 is above 5 volts.
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