MSD and other CDI ignition half-truths

[Dylan]

From what i understand ICE is an inductive system as per factory set ups. I think they run a better coil and also run the coil at 16 volts to achieve there better spark output.

[Circlotron]

All ICE systems are inductive, no CDIs. 16 volts is an option with the 7 amp units, the 10 amp ones can run with a 24 supply. Their secondary voltage risetime is about 12 microseconds from memory - CDI can be faster but you risk crossfire when adjacent plug wires start talking to each other.

[Circlotron]

Did a youtube comparison between a MSD6 and an inductive discharge ignition today. The difference in spark duration between the two is notable. Also the space between the multi-sparks where nothing is happening is visibly just as wide as I measured with the scope.

MSD6 http://youtu.be/P-QA-GuAz1w

Inductive http://youtu.be/Jcqeuhdbgv8

[VL400]

Impressive test setup Really shows the difference of CDI compared to inductive spark duration.

[delcowizzid]

circlotron do you have any camira style ignition modules im wondering if you can do a test for me with your flash dizzy tester .its been brought to my attention that there are a few different part number modules and some add upwards of 6 degrees of timing at higher rpm ide like to find a part number with the least amount of timing shift

[VL400]

You can adjust that using "EST params - Time domain correction to spark" in 12P.

It allows for the processing delay of spark delivery, so if you get this to match there will be no timing advance/retard from commanded as the revs increase.

Need to lock timing to a fixed angle using a mode 4 command and increase revs while watching with a timing light and adjusting the spark correction value.

[delcowizzid]

yeah i know the setting is there but it seems they hold steady till 4500 then just suddenly add 6 degrees.one module part number actually retards 2 degrees.ill have a play with the timing light and see what i can do

[VL400]

Ah ok, thats a bit odd and cant fix that with software.

Have seen odd timing shifts with the reluctor wired in reverse.

[Circlotron]

I haven't got any Camira modules but if you want to send me one or more and a suitable distributor I'll spin it up for you and see what we get. PM me for details.

Mag impulse distributors can vary a bit from one type to another so for best results you really have to treat the distributor and module as a pair. Different distributors of the same type probably not an issue though.

[VK_3800]

Have seen odd timing shifts with the reluctor wired in reverse.

Probably jumping to the wrong post on the cap, if you wire a reluctor to an MSD module (e.g. 6A/6AL) it will fire halfway in between.

Just for the record I'm still a fan of a good high energy CDI system, I've had stuck fuel bowl needles causing fuel pooling in the bottom of the manifold and it still fires, can't flood it to the point of not running. Obviously if the mixture fails to ignite then duration is an issue, but if it does ignite reliably then I don't really see a problem.