CDI ?.... MSD ?..... Help please

[Barry]

Andy, does that mean you have fairly long HT runs back upto the engine bay (if installed as illustrated), and if so, would there be an argument in favour of running the relatively low tension leads (MSD output) back into the bay, and dressing the MSD coils to represent the orginals?

Or is it that the MSD coils are too different (dimension-wise) to be made into Bosch looky-likeys?

Hope you're well BTW .

[MBEngineering]

HI Lightweight_911
If you are to put the setup you have in the photo on the rear baulkhead, you will need to fit the MSD coils upright, as thay are not desined to be fitted on the side or on the fan housing upside down, thay will fail in this position, unless you specified coil positioning when ordering, more info hear http://www.msdignition.com/.

regards mike

[Barry]

I'd better mail James (TheEasyLife) then: I'm sure I put my MSD coil in the original coil's position.

Actually, thinking about it, I seem to remember that it was a non-MSD made, but compatible coil: I wonder if that's why it's been O.K.?

[Bob_Salmon]

Neither - split the MSD output and feed each coil from one lead of the splitter (see the white wires in the picture from Mike above).

Yes, that's parallel then: I'm amazed that the unit can take this, as effectlively it means that the internal gubbins must be 'engineered' (if that's what electronics are) to run either one or two coils with no physical switching, which is either very impressive, or just a worry for their warranty department .

Nevertheless, I do know that MSD units have a name for operating in some dreadful conditions in some of the U.S. based applications, and doing so for long periods without trouble.

As per the above question (sorry Ian ), I'd love to know what dictates the cut in / out point of the multi-sparking function, before it drops into the big, single spark mode. I.e. whether this is simply a function of revs, or a function of stress upon the unit (more load, less multi-sparking).

Isn't it just a question of how long it takes for the capacitors to re-charge each time? At lower revs the MSD unit can power several sparks but as the revs increase so the number of pulses available at the plug are reduced.

Bob

[Barry]

Absolutely, I'm just wondering whether doubling up on the coils affects this (i.e. current draw), or if it's purely a function of number of cylinders and revs (i.e. discharges per minute), regardless of coil numbers.

EDIT: Sorry, so you're saying you'd expect the multi-spark 'zone' to be un-affected because as far as the capacitor is concerned, it has simply dumped it's charge (and doesn't care where to. just as long as the charge is gone), and is ready for re-charging, irrespective of single / twin coils?

[Bob_Salmon]

Absolutely, I'm just wondering whether doubling up on the coils affects this (i.e. current draw), or if it's purely a function of number of cylinders and revs (i.e. discharges per minute), regardless of coil numbers.

EDIT: Sorry, so you're saying you'd expect the multi-spark 'zone' to be un-affected because as far as the capacitor is concerned, it has simply dumped it's charge (and doesn't care where to. just as long as the charge is gone), and is ready for re-charging, irrespective of single / twin coils?

That's my understanding Barry. That said, I still haven't installed my own MSD stuff - still trying to work out where best to fit an odd mixture of an oversize 6TN spark box with external rev limiter and tacho driver, plus a longer coil (the Blaster 3), so it's just theory at this time................

Bob

[Barry]

That certainly now makes sense Bob .

Mind you, the single / twin MSD is a question only the twin spark folk need to address, so I guess us mere mortals don't have to worry about that particular question (other than pondering the theories for fun ).