Tracy Crook wrote:

 >bryan.wilkinson wrote:
 >>
 >> Paul ,
 >>
 >> Lookd over this old article on off the peg VW cconversions { beefier
 >> crankshaft mainly & shimming of cylinders } can't remember  company name
 >> but from an old 1991 magazine.
 >>
 >> Anyway  - it seems magneto's give a longer duration spark than EI - so
 >> how do you get this with electronic ignition ?:^/ I would have thought
 >> this would be standard stuff these days for emissions purposes anyway
 .......
 >>
 >> Bryan

 >Its called Multiple Spark capacitor Discharge.
 >
 >There is a MSD brand of electronic ignition system here in the states
 >that is very popular.
 >
 >Paul Lamar

 At the risk of injuring some sacred cows I'll put in my  $.02  here.

 True, MSD (multiple spark discharge) is the only way to get long duration
 with CD type ignition and MSD (the company) makes a fine one.   This is as
 compared to "regular" CD which gives a very short duration spark.  The price
 you pay is the  weight of this system and high power consumption as well as
 a pretty hefty price.

 It should be pointed out that electronic ignition is not synonymous with CD.
 Most all cars are equipped with "EI" these days but this just means that the
 timing and switching of the coils is done with electronics instead of
 mechanical points.

  Inductive Coil ignition (as opposed to CD) inherently gives a nice long
 duration spark which is important when doing lean burn combustion (what you
 should be doing 95% of the time in an airplane).  Magnetos give a longer
 spark than straight CD but usually less than inductive coil ignition.

 Another factor in ignition is energy in the spark.  CD (especially msd type)
 is potentially the highest here but there are exceptions.  The Ducati  CD
 used on Rotax engines is so weak that its hard to see the spark in daylight.
 I know people who have spent days trouble shooting this ignition system
 (because they couldn't see the spark) when there was nothing wrong with it.

 The energy in Inductive coil & magneto type systems depends on the
 particular coil involved.   Magnetos are usually at a disadvantage here
 because of the small coil size.   The 86 - 92 Mazda coils are relatively
 high energy type (and this is reflected in their weight).

 My advice to those using the Mazda rotary for aircraft use is to use the
 stock coils unless you have a very compelling reason not to.   In the RPM
 ranges we are interested in (about 6500 rpm max), there is very little
 advantage to using anything else.  Those who claim that there is a world of
 difference when using something else are either talking about operation at
 the far end of the performance spectrum or they are dreaming.  Gains due to
 ignition changes are purely due to improvements in efficiency (which is
 wonderful) so don't you think Mazda would have done this is the improvements
 were this dramatic?  They were so desperate for efficiency gains during the
 design of the second generation RX7 (1986 - 1992) that the project was going
 to be cancelled if they didn't find a way to reduce the car weight by ONE
 GRAM per design  team member.  They sweat bullets and spend millions to do
 that.  Trust me, if a better ignition system would have done the job, they
 would have done that instead.

   True, there IS a big difference if you are going to run at 9000 rpm (like
 the Racing Beat 3 rotor project) but the average airplane builder would be
 wasting their time (& money) going on a quest for the ultimate ignition
 system.  But, (as Dennis Miller says) that's just my opinion, I could be
 wrong  :-)

 Tracy Crook
    rws@altavista.net
 Web site:   http://www.rotaryaviation.com

   When I first started flying my coot I was using an MSD on the
leading ignition and the trailing was stock but the life span on the
trailing plugs was half that of the leading and they would foul easy
when I used 100 LL.
  I then installed MSD on the trailing and the life span on the
trailing plugs came up to the same as the leading plugs.
  In the last days that the old coot was flying I used two MSD units with
the leading crank trigger that fired two MSD coils that fired the
leading plugs and the trailing had a single MSD that fired coil that
went through the distributor cap and rotor.
  I am sold on the MSD units and would not consider running without one.
  Ken Welter

 
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