[Spits] pertronix

[Greg Rowe]

I
replaced my dead Crane unit with a Pertronix about a year ago.  I didnt
remember there being any difficulty
with determining which Pertronix to get,
however there was a lot of confusion
about the right ignition coil.  You may
already know this but if not, it may help.
Pertronix
talks about 1.5ohm and 3 ohm coils which correspond to 6 volt and 12
volt coils
(the 12 volt necessarily has more windings which results in the
higher resistance).  Depending on what year/model you have, your
spitfire may
have come originally with either a 6 volt or a 12 volt coil.  In addition, it
may have been changed by a
previous owner so double check.
Both
coils put out the same voltage out of the ignition wire to the
distributor, the
difference is the voltage that they need to operate, the
amount that should be
seen on the + terminal.  You may wonder
why Triumph
would use a 6 volt coil in a 12 volt system and that is because
when you are
starting, the heavy draw of the starter (and lack of alternator
charging)
reduces the available voltage below 12 volts.  You get a hotter spark to
assist with the
difficult task of firing the engine by temporarily overloading
a 6 volt coil
than underloading a 12 volt one.
So
normally a 12 volt coil gets 12 volts (nominally) ALL the time on its +
terminal.  The 6 volt gets the full 12
volts when cranking and then only 6
volts (through either a ballast resistor or
ballast wire) when running.
What
does all this have to do with the Pertronix unit?  When you install the
Pertronix, it will tell
you to hook up the red wire at the + terminal of the
coil and the black wire at
the - terminal.  It will also tell you
that you
need a 3.0 ohm coil, e.g. 12 volts. 
No one that Ive spoken with is really
sure, but it appears that
Pertronix is saying that their unit needs a constant
12 volts to operate.  The coil is a convenient place to take it
from even
though youre really just using a common junction, theres nothing
magical
about the 12 volts at the coil as compared with anywhere else (although
you do
want it to be switched in synch with the ignition).  And I cant think of
anything special about
the   terminal, the Pertronix is just grounding the
coil so it produces a spark
and I dont see how the unit could care whether
the coil is 3 ohms or 1.5.  So what I did was leave the 6 volt coil in
place
and take a 12 volt source for the red wire from the Pertronix from the
remnants of the factory electronic ignition.  So far thats worked.  Ive also
heard that some folks have just run
the Pertronix on 6 volts and it seems to
work but whether it shortens its life,
who can say?
So
bottom line:

If
you have a 12 volt coil and no ballast wire, you are good
to go.


If
you have a 6 volt coil and a ballast wire, you can


-      
Bypass the ballast and replace the coil with a 12 volt (lose
advantage of hotter spark when starting)


-      
Keep the 6 volt and find another 12 volt ignition source for the
Pertronix (not recommended by them but seems to work)


-      
Keep the 6 volt, hook up to 6 volts and see if it actually makes a
difference (uncharted waters).

I
hope this helps.  Good luck with it! Greg Rowe
 > From: dave at ranteer.com
> To: spitfires at autox.team.net
> Date: Tue, 14 Jan 2014 16:56:34 -0600
> Subject: [Spits] pertronix
>
> hi.  have a 75 spit; was converted to allison ignition which is pretty
dead.
> I want to order a pertronix, but it appears there are numerous choices.
>
> how do I choose????