Distributorless ignitions

[Ed Lansinger]

Bill Lewis wanted to know what the reason is for the big push to distributorless 
ignitions.  I can't give a definitive answer but I'd like to propose the following 
possibilities:

1. The distributor cap size vs. ignition voltage argument sounds reasonable.
2. Maintenance is reduced if you don't have to set mechanical timing.  The timing also 
won't slide out of whack.  The new standard is "no tune-ups for 100,000 miles" so every 
little bit helps.
3. A coil pack just might be less expensive in production than a distributor.  Think of 
not just the unit cost but the cost to prepare the engine for it and assemble it to the 
car.  Plus it's something that must be designed into the engine to begin with.
4. You get more reliable spark if you eliminate the extra gap in the distributor and 
the associated wear and oxidation you get on the rotor and wire terminals.
5. You get a much larger range of control over your spark advance values.  This is 
important for engines that might run 40-50 degrees of advance at light loads.
6.  You don't have to worry about an increasing spark gap in the distributor as advance 
increases.  Just for grins I recently cut a slot in the distributor cap of my GLH Turbo 
so I could watch the position of the rotor as the spark fired.  At high RPMs the rotor 
wasn't directly in front of the wire terminal, so the spark had an extra long gap to 
jump.  I adjusted it as best I could but now I'm marginal at idle and definitely off 
during crank.

Steve ("=Ravet") asked if in a wasted spark system do both plugs fire from one coil 
discharge.  The answer is a definite yes.  The current loop is out one terminal of the 
secondary, through the center electrode of a plug, jump the gap to the ground 
electrode, through the head to the ground electrode of the paired plug, jump the gap to 
the center electrode, and on to the other terminal of the secondary, completing the 
loop.  The situation is helped if one cylinder is on its exhaust stroke because the 
resistance of the hot, ionized exhaust gas is much lower than the intake gas so you 
don't waste too much energy.  Of course, this doesn't help you during crank...

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Ed Lansinger
General Motors Powertrain
Powertrain Control Center
Premium V Software & Calibration Group
Milford Proving Ground, Milford, MI
elansi01 at mpg.gmpt.gmeds.com  8-341-3049  (810) 684-3049
The opinions stated above are mine, not my employer's.
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