MSD and other CDI ignition half-truths

[Holden202T]

I'd be very interested to see the test results of an LS1 coil compared to the above info!!

This kind of coil -> http://www.knology.net/~rv7rotary/13_1_b.JPG
Same 1700 volt zener load string.
Internal coil driver limited at 8.3 amps.
Results:-

Yeah that's the ones!! That's good to see, cause we are running one of them on a 202 with vl400's lsx driver board I know ls2 are heaps more powerful

I would also like to see ls1 coil tests. I think ls2 are overkill for most applications but would be interested in them too.

So your saying my 6 x ls2 coils in wasted spark config is no good

[immortality]

See, that has me thinking, would it be beneficial to run the Delco LSX driver and LS2 coil on the 304 instead of the factory ignition module/coil?

[Circlotron]

Not quite that simple. The factory 304 module has an extra wire from the ECU that tells the module to take trigger pulses either directly from the distributor during cranking or limp home mode, or a processed version of that same signal that goes through the ECU first.

[Holden202T]

yeah it would work, all the driver board does is converts the normal coil signal to what the LSx coils need to fire, all the ecm control etc still works, however in testing of this with various coils we started with LS2 coil and it did work ok for a while but then just stopped running one day, and the coil was red hot and after that it never worked again .... VL400 did some bench testing and it seems to LS1 coil doesn't suffer this same problem so we are now running it on that!

[VL400]

Some good testing circlotron. In your first post, is the scope trace the current on the secondary side of the coil? Just inverted due to the neg voltage? Not trying to defend MSD as I think they have been clever with marketing more than having top notch bullet proof parts, but I wonder what it would look like firing an actual plug in a compressed cyl full of fuel and air? Am a bigger fan of ICE stuff, he makes some excellent gear.

The MSD 6AL2 is also around a 1ms duration for a spark cycle, but it does vary a little with RPM as its changes the number of multiple spark events at low RPMs.

If you want a few different LS2 coils to test, flick me a PM.


The LS2 coils without an external heatsink do not work in single coil apps due to the heat it produces internally, which it struggles to dissipate. Even on low dwells they just cannot handle the duty cycle LS1 coils get warm but are bolted to an engine so its to be expected, they do produce a significantly smaller spark output for the same dwell time though.

[immortality]

So then, what would be the best combination for a fairly stokish 304.

Factory ignition module and good quality coil.

Or MSD 6AL with good coil (I have these laying around)

or PCM hack LSX module with LS coil?

[Circlotron]

Yep, the trace is negative secondary current @ 100mA per div. I have 41 pcs of 1.5kW 39 volt TVS diode in series for approximately 1600V-1700V load. I chose that voltage because it is about the same drop as one of those HEI test plugs. http://www.pirate4x4.com/forum/attachme ... i_test.jpg One advantage of the zeners is it is very consistent frm one cycle to the next. The plug is a bit of a negative resistance in that when you push it harder the voltage drop decreases somewhat.

The other scope screenshots are secondary current, secondary voltage and the purple trace is the integral of volts x current to give energy in millijoules.
Not always very consistent with trace colours vs what is measured though! Also check different time/div for different pics.

AFAIK with the 6 series ignitions the power end is much the same but they differ in the low signal side of things. The 7 series ignitions dump the cap but has an inverse diode across the SCR to let it resonate several half cycles so the output current alternates. Doesn't suit my test jig at this point.

As for coil losses with CDI, for the sake of round figures if you have a coil secondary resistence of 4000 ohms and a peak current secondary current of 400mA then you are going to drop 1600V in that intrnal resistance. And if the load clamps the output voltage at 1600V then voila, half your power is being lost in the coil secondary. Add several K resistance for the plug leads and you can see where this is going. Say you have 1/3 the current with an inductive discharge setup you will have 1/9 the losses. Roughly sorta kinda.

[Circlotron]

Not quite that simple. The factory 304 module has an extra wire from the ECU that tells the module to take trigger pulses either directly from the distributor during cranking or limp home mode, or a processed version of that same signal that goes through the ECU first.

Also, I misunderstood what was meant by Delco LSX driver.

[Dylan]

So then, what would be the best combination for a fairly stokish 304.

Factory ignition module and good quality coil.

Or MSD 6AL with good coil (I have these laying around)

or PCM hack LSX module with LS coil?

I fitted an MSD 6A digital with MSD coil to my 5 litre with hi comp and a rich idle mixture it made wonders to idle quality and smoothed out the rev range. Previous ignition was standard with good condition components.

[immortality]

AFAIK with the 6 series ignitions the power end is much the same but they differ in the low signal side of things. The 7 series ignitions dump the cap but has an inverse diode across the SCR to let it resonate several half cycles so the output current alternates. Doesn't suit my test jig at this point.

As for coil losses with CDI, for the sake of round figures if you have a coil secondary resistence of 4000 ohms and a peak current secondary current of 400mA then you are going to drop 1600V in that intrnal resistance. And if the load clamps the output voltage at 1600V then voila, half your power is being lost in the coil secondary. Add several K resistance for the plug leads and you can see where this is going. Say you have 1/3 the current with an inductive discharge setup you will have 1/9 the losses. Roughly sorta kinda.

So what is the difference between the ICE cdi ignition and all the others as it seems the ICE stuff doesn't drop the output of the coil?