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MSD DIS-2 / Crane hi-6 di2 308 application

Discussion in 'Technical Q&A' started by Ferraripilot, Jul 14, 2009.

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  1. Ferraripilot

    Ferraripilot F1 World Champ
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    #1 Ferraripilot, Jul 14, 2009
    I just had a conversation with a tech at MSD regarding this system for use in my 308. I currently have both banks fired by two Crane xr700 optical ignitions mounted into one distributor. I would like to have both xr700s trigger a DIS-2 which has the ability to fire both coils and control ignition advance. I would have no problem hiding one box and I like the stock look otherwise I would go for Nick's awesome system (can't stand the way it looks though). The tech specifically advised it would not work because the way these engines fire does not give the DIS-2 enough crank rotation to ‘recharge’. He said they require 20 crank degrees to recharge and I have no way around this other than to just use two MSD 6a boxes. I thought our engines fired every 45 degrees? Is this not enough recharge time?

    What does not make sense to me is that CD boxes are used in multiple cylinder applications all the time. The DIS-2 is specifically designed for 4 cylinder applications which use 2 coils with two terminals for each cylinder. The coil fires both sparks plugs with one firing for the compression stroke and the other is a ‘waste spark’ for the exhaust stroke. My application is a DIS-2 firing two coils 4 times each engine rotation. The capacitor inside the DIS-2 is the same which is used in a 6a which fires 8 cylinder engines on its own all the time.

    Is anyone able to offer me another explanation for this, or is the MSD guy making perfect sense only I am just not getting it.
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #2 Steve Magnusson, Jul 14, 2009
    Last edited: Jul 14, 2009
    Seems a little strange that he would quote "minimum crankshaft degrees between firings" rather than a "minimum time between firings" (i.e., crankshaft degress/RPM), but, if their DIS-2 system is specifically designed to run a 4-cyl, it would have to be way over-designed (by 2X) to run an 8-cyl engine at a similar maximum RPM (so it makes sense to me that he says "not possible" to use on a V8 at ~8000 RPM unless the DIS-2 can run a 4-cyl at 16,000 RPM). You are asking for the DIS-2 to fire two coils (simultaneously) 4 times each engine rotation, but, on a 4-cyl, it is firing two coils (simultaneously) only 2 times during each crankshaft revolution.

    PS A V8 fires a cylinder every 45 deg of camshaft rotation (i.e., a V8 fires a cylinder every 90 deg of crankshaft rotation)
     
  3. Ferraripilot

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    #3 Ferraripilot, Jul 14, 2009
    Being an application for 4 cylinder engines, yes, I sort of understand. What I do not understand is that the capacitor inside the DIS-2 is the exact same capacitor which is used in a 6al which powers V8 ignitions all the time. The DIS-2 just uses components to allow the signal to be split between two different signal generators which essentially makes it perfect, in theory, for a 308 application
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #4 Steve Magnusson, Jul 14, 2009
    But on the "typical" V8 application, it is only firing a single coil (so the total average power delivered is the same as a 4-cyl using the waste spark arrangement - so this is why it works OK in either system). What you are trying to do (8-cyl with waste spark) requires 2X the power. The DIS-2 spec does say that (in theory, at 14V supply) it can get to 15.5K RPM so that might cover getting a V8 to 7.5K RPM, but (even if you had a way to always supply the higher voltage) I think that you'd have to have a very good power supply/wiring arrangement and a great heat sinking arrangement (for the DIS unit and the coils) to maintain any reliabilty.

    However, please describe your overall system more completely -- I'm having a hard time seeing how you can do a waste spark system on a V8 with only two coils? (i.e., on a 308, when cyl #1 fires, the only safe place for the waste spark is in cyl #4 -- if you route the waste spark into the 5-8 distributor that wouldn't really work).
     
  5. Ferraripilot

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    #5 Ferraripilot, Jul 14, 2009
    I cannot do a waste spark system with what I have, but the DIS-2 is designed to work with two coils which fire two plugs each in a 4 cylinder application. I am essentially asking the DIS-2 to double its job which I guess is not doable.
     
  6. Dandy_Don

    Dandy_Don Karting

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    #6 Dandy_Don, Jul 15, 2009
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    I had the same reservations about the looks of Nick's system but it can be overcome. I mounted the coils on the firewall near the clutch bellcrank. I left the single distributor in place and then routed 4 plug wires (front bank) through fake spark plug boots mounted on Euro dist cap. If you look real hard you can see around this but it looks pretty good. I will post pix tomorrow. Once you go to Nick's system you will never need to fool with all that junk anymore. I am even thinking of selling my Euro Distributor because it really is not needed at all. It is so nice to be able to adjust your timing in 3-5 seconds while the car is running than the old way. And trying to get both banks firing right using 2 Crane pickups is a LOT harder than it seems. Basically you guess what is 45* and then put it back together and try it, then tear it out, try it again. I spent one whole afternoon getting mine right and then something else was a problem, oh yeah, advance. It is just not worth it. For ease and reliability get Nick's system and never think about your electrical firing system again. I will post pix tomorrow.


    Don
     
  7. Ferraripilot

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    #7 Ferraripilot, Jul 15, 2009
    I set up both Crane xr700s pretty easily using the flywheel marks. What I first did was arrange the first optical trigger to fire when lined up with the mark/slot on the distributor itself. I used this mark as my point of reference for 7 btdc on the flywheel and had the engine sitting 7B TDC then fitted the distributor. I scribed a mark on the distributor housing as a point of reference for the other trigger mounted inside for the opposite bank. All I had to do then was set the engine at 7BTDC for the other bank and line up and fiddle with the trigger inside until it fired according to the marks. worked perfectly
     
  8. luckydynes

    luckydynes F1 Rookie

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    #8 luckydynes, Jul 18, 2009
    I'm familiar with the DIS-4 but not the DIS-2. If it's laid out like the DIS-4 the problem is these units have built in rev limiters which are scaled based on the number of times the input gets charged. Before I got my coil on plug system working I tried to use a DIS-4 to run my dizzys. If I would have maxed out the rev limiter to 16k rpm I could've made it work to 8k (not sure if 16k was max rpm ... think it was 14k come to think of it which meant 7k redline which is to low for me) so max rpm will be "halved" with the DIS-2.

    cheers,

    Sean
     

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