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Ignition


Just to set things straight:  I have a COMPUTERIZED ignition system, not a 
capacitive discharge system (CD).  There is a *very* big difference between 
the two!

As for the energy output, to quote Dr. Jacobs, "It's not that simple."  A 
big ol' blast of electricity isn't always the answer.  Too much spark will 
cause cavitation, which is when the spark punches through the fuel mixture 
so hard that it actually pushes it away from the spark and it doesn't 
ignite.  Too much spark will also reduce the life of a spark plug.  Also, 
ignition requirements vary not only on RPM but on the density and 
temperature of the fuel mixture as well as spark plug conditions (like a 
fouled plug).  It's not that simple.

The stock system, of course, does provide plenty of energy and it does what 
it has to well -- for stock I'd use nothing but Bosch.  But that energy 
isn't fully utilized.  With my system my performance times have increased 
slightly and so has my MPG.  I'm still in the process of data collection so 
I don't have all the figures yet, but my MPG went from 14 city 17 highway 
(stock ignition system) to 16 city 21 highway (computerized ignition, stock 
wires, plugs not indexed).  Obvious advantage:  For a car that drinks 
nothing but 92 octane the computerized ignition has already begun paying 
for itself.

     Toby Erkson
     air_cooled_nut@pobox.com
     modified '72 VW Squareback 2.0L
     stock '75 Porsche 914 1.8L

______________________________ Reply Separator _________________________________
Subject: Re: Rebuild 1600 engine troubles... long.
Author:  type-3-errors@umich.edu at SMTPGATE
Date:    1/1/97 8:57 PM

...In the end the question was settled
by someone who had bothered to look up in their Bosch Electrical Systems
Handbook to find how much energy was actually NEEDED to accomplish the
ignition task.  The end result was that the conventional system provides a
MINIMUM of TEN TIMES MORE energy than is needed at ANY RPM under 6000.

I love CD ignitions.  And I don't really aspire to be classed as a
retrogrouch in this issue, but the advantages of electronic ignitions really
lie in reduced maintenance and long term stability.
...


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