I have always been keen on 4 channel DIS/Wasted Spark as there are nice aftermarket systems available from the likes of MSD. Here's what I think, please tell me if I'm wrong: DIS probably delivers the best spark for my needs, as EDIS like other OE components will be produced with a cost vs performance trade off. i.e. I doubt that stock EDIS can match 4 ch DIS. (maybe true for RPM: EDIS is said to be limited to 6500..8500 RPM depending on EDIS model, and hard to get info on that).

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Spark energy market

Note that there is a lot of aftermarket bullshit in this topic all over the market. You get 0.00 engine power increase (you get some added sparkplug wear instead) if your spark ignites the mixture reliably, and you increase spark energy further. It is more important to get the required spark energy over the RPM range (electronically controlled ignitions usually work well through the RPM range), and over the VBatt range, preferrably from 6.5 .. 16V (but some systems don't measure VBatt at all).

What is more important is tuning your spark timing. Good tuners can tune within 2 degrees of optimal advance (which is max power within the knock-safe area). Some tuners claim they can tune within 0.5 degree, but this usually comes from incompetence (not knowing they have to retune after tank refill and environment humidity change). Aftermarket spark amplifiers usually forget about spark timing, because it cannot be simply adjusted automatically (cheaply) without risks. That's why aftermarket spark amplifiers stay with the safe spark-energy-boost functionality, which doesn't help, but doesn't risk too much at least. And a little added sparkplug wear never hurts (especially for dealers).

More spark energy is often good. I think that about half of all new cars have to weak ignition systems and they will benefit from a good aftermarket system. A strong ignition system also makes it possible to use a richer mixture without loosing tons of power. (Jörgen)

Might be: that means they configure the dwell with not much margin for too rich mixtures. With a configurable controller like GenBoard/VerThree you can simply adjust dwell to your needs - assuming the components (transformer and IGBT) are not overstressed already.

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Here's the 4ch DIS specs:

:MSD DIS-4 (4 Channel Ignition) - PN 6215

:DIS OPERATING SPECIFICATIONS

:Spark Energy: 105 - 115 milliJoules per spark

:Primary Voltage: 460 - 480 Volts Delivered to Coil

:Output Voltage: 40,000 + Volts

:Spark Series Duration: 20° Crankshaft Rotation

:Operating Voltage: 12 - 18 volts, neg. ground

:Current Draw: 7.4 amp @ 10,000 rpm

:RPM Range: 14,000 rpm with 14.4 volt supply

:Weight & Size: 4.5 lbs., 9.5"Lx4.5"Wx2.2"H

:MSD Blaster DIS Racing Coil PN 8230* (one per cyl used)

:BLASTER SPECIFICATIONS

:Primary Resistance: 0.080 ohms

:Secondary Resistance: 1.8K ohms

:Maximum Voltage: 37,000 volts

:Turns Ratio: 70:1

:Peak Current: 570 mA

:Spark Duration: 130 Us

:Tested with an MSD DIS-2HO Ignition

If the 0.08ohm primary resistance figure is right for the coil I don't think that you'll have a living DIS-4 for long! I run my DIS-4 for with two 0.7ohm coils in paralell on each channel and that is on the edge. (Jörgen)

Also, I can buy aftermarket EDIS coils:

:MSD Ford Coil Pack, 4-Tower for 1995-1998 PN 8241

:BLASTER REPLACEMENT SPECIFICATIONS

:Primary Resistance: 0.53 ohms

:Secondary Resistance: 12.8K ohms

:Maximum Voltage: 40,000 volts

:Inductance: 5.8 mH

:Turns Ratio: 83:1

:ACCEL FORD SUPER EDIS COIL PACK FOR 1999-89

:Specifications Tested with Ford EDIS system

:Primary Resistance 0.5 Ohms

:Secondary Resistance 11.6 k Ohms

:Turns Ratio 85 : 1

:Maximum Voltage 42,000 volts

:Peak Increase in Energy vs. OE: 11%

:Peak Increase in Voltage vs. OE: 8%

:Peak Increase in Arc Duration vs. OE: 7%

:Peak Increase in Current vs. OE: 9%

Answers to these questions will help me decide:

EDIS

42,000 volts is nice but how's the current i.e. can OE EDIS deliver as much current?

What's the output (coil driver) voltage from a OE EDIS (anything like 460 - 480 volts)?

I want to use the MSD crank trigger, which has only 4 VR cycles per revolution. (Good)

So, can I use one of the misc outputs in GenBoard/VerThree to emulate the 36-1 VR signal to the EDIS?

No. Fortunately wouldn't make sense anyway, when you can drive the coils from the onboard drivers, with higher RPM limit and less possibilities of error. The OutputTrigger is only good for HW (and maybe installation) testing, not driving production units.

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DIS

What are the output specs (pulse voltage/energy, duration, etc) for GenBoard IGBT drivers?

The recommended IGBTs clamp at 380..400V. The traces are not recommended for much higher than that anyway (although I've seen them being used for 1000V). The primary of the coil never sees such high voltage anyway while the sparkplug is connected to the secondary side (a bit theory: the sparkplug on the secondary side limits the voltage, so the voltage on the primary side is limited proportionally, with the turns ratio, 1:80 or 1:100 typically).

Can I use 2 IGBT drivers in paralell to increase output to coils?i.e. 4 * 2 IGBT?

It is very easy to use a small onboard wire to drive the gates of 2 IGBTs simultaneously from the same ign259 signal. But 1 IGBT, with 14A current per channel should be enough. That is about 14V*14A/2=98W max power (with approporiately matched, ideal coils) per channel (!). At 6000 RPM (50 sparks/sec) that is almost 2000 mJoule per spark, more than 20 times of what is already skyhigh spark energy. In practice 1 IGBT is enough for an 8 cyl distributor setup too, and 4 or 8 IGBTs will just drive the sparks of 8 cyls while laughing.

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Ion Sensing HW designs are springing up and amongst them is some multiple board architecture. I'm gonna think about this some more...along the lines of keeping ignition, ion and data logging loosley coupled to meet race regulations...i.e. all boards connected during testing, disconnected during competition. e.g. Ion Sense learning and writing curve for timing offline.

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Questions

I'm trying to finally decide on a coil. I'm going to use a wasted spark setup using 4 IGBTs & 4 coils. I would like to use the MSD 8421 but it's primary resistance seems too low at 0.53 ohms (as do most coils at around 0.5 ohms), I expect that I need about 1 ohm otherwise I will fry the IGBTs and maybe the PCB (with 26A).

What can I do to address this? Can I add a ballast resistor before the coil?

0.53ohm is ok, the dwell is controlled to charge the coil until a certain current is reached. In other words, it takes time for the current to reach 26A and we don't let it. A series resistor can be used if you want to feel safe. -Jörgen

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Any and all answers/ideas/opinions greatly appreciated :)

Thanks, Patrick.