Re: Ignition and sparks

[Theo Smit <theo.smit@dynastream.com>]

MSD does two things. First, below 3000 RPM you get multiple spark 
events, which is helpful in preventing misfires and the resulting plug 
fouling. At high RPM, the high coil primary voltage (up to 300 or 400 
volts) saturates the coil even though the time between ignition events 
is drastically reduced. Conventional coil drive systems lose most of 
their fizzle at higher RPM, and this can lead to high speed misfires. 
I'm not saying that they are a cure-all, and you are correct that 
without a good timing reference the battle is lost from the outset, but 
the MSD systems and their ilk do provide useful benefits besides the big 
decal. A system like the MSD6AL also includes a rev limiter, and if 
you're at all interested in running your car in track or autocross 
events, then a rev limiter is an absolute must.
You can use the optical sensor from the Allison system to trigger the 
MSD input as well, and get the benefit of more reliable ignition 
triggering plus the improved coil firing that the MSD offers. No sense 
in going halfway...

To answer Barrie's comment - the problem with ignition is that the 
typical engine cylinder is not a big room filled with an explosive 
mixture - it has rich spots and lean spots all swirling around. If the 
coil fires when there's a big glob of fuel hanging on the electrodes, it 
won't fire the plug... and it also won't fire if the mixture at the 
plug, at the firing instant, is 25:1. The multiple spark business gives 
you better odds, and it does actually work. You just have to decide 
whether or not it's worth the $130 or more to get it, and I do agree 
that if you're on a budget, then fix your distributor first, and install 
an Allison, Pertronix, GM, or other points replacement trigger and 
amplifier.

Best regards,
Theo Smit

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