Is Pertronix flame thrower coil compatible with CDI?
 

I recently converted from conventional points to Pertronix Ignitor points. I chose this opportunity to also install a Pertronix Flame Thrower coil. After the install, the car wouldn't start. I swapped the original coil back and the car runs now.

I went through several wiring attempts before landing on the right one, so now I'm wondering if I fried the Pertronix coil, or if it just wasn't compatible with the CDI from the git-go.

Most likely NOT.

My guess is that the new "points" were designed to closely simulate actual mechanical points, somewhat lucky it worked with the CDI. On the other hand the Flame thrower coil with single "I" core is likely designed to be used as directly connected to the points, not driven by a CDI.

Optimally, any CD ignition should be coupled with a E & I core "transformer" type of ignition "coil".

The traditional Kettering ignition coil operates quite differently vs what is required of a CD ignition coil. Spark energy is stored in the kettering coil over a period of time, while the points are closed, and then released to form a spark upon point opening.

With a CDI the energy to the inductive primary must be "force-fed" (ELI the ICE man) 300-400 volts applied, in order to quickly (overcome the primary inductance) provide a strong enough magnetic field in the E & I iron transformer core resulting in spark energy in the secondary.

This is NOT to say a kettering type coil will not function, just that for optimal advantage of a CD ignition a transformer type ignition coil should be used.

I have a Pertronix 45111 epoxy-filled coil on my CDI system and it seems to work fine (although I do have some other CIS running issues that may eventually lead me to this thing). Primary and secondary resistance of this coil appeared to match the specs of the stock coil.

Interesting thought on the internal winding arrangements; I'll have to investigate that further.

wwest is wright cdi works whith transformer.Youre Lucky you diden fried your cdi.

Hmmmm....OK - Going to not drive mine anymore until I research further.

Quickstep - Sorry about doing a minor hijack on your thread. I'll share what I find.

OK - I found the posts I remembered using for reference back when I sourced the Pertronix 45111 - Here's are the links:

http://forums.pelicanparts.com/porsche-911-technical-forum/163259-cdi-coil-confusion-please-help-my-poor-sc.html

http://forums.pelicanparts.com/porsche-911-technical-forum/642219-jacobs-coil-my-cdi.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/714237-simple-question-can-you-run-oem-coil-msd-6al2-cd-box.html

From this, it seems the specs of the original CDI coil are:

input resistance: 0.4-0.6 ohms
secondary resistance: 650-790 ohms
turn ratio: 100:1
inductance: ~2mH (measured)

The specs for the Pertronix 45111 (which, incidentally, is advertised by Pertronix as suitable for CD ignition systems):

input resistance: 0.6 ohms
secondary resistance: 9000 ohms
turn ratio: 100:1
inductance: 6.0 mH

Pertronix specs:

http://www.pertronix.com/catalogs/pdf/ptx/2012/ptx2012_coils.pdf

I saw limited risk in trying the Pertronix coil; the input load to the CDI box appeared the same. The only down side I saw was that the higher inductance may cause trouble at higher RPM (less spark duration?). I do have some CIS trouble as I mentioned above, but that is <3k rpm.

My only "testing" (other than a running car) was to run a coil wire to an old wide-gapped spark plug, ground the plug base, and spin the motor with the starter. I observed very fat spark at 0.080" gap. Granted, that's easy at start-up speed. Who knows what it looks like at 6k rpm at normal gap (but I haven't heard the thing miss at high rpm yet).

One motivation I had to use the Pertronix coil was that it is epoxy-filled. The coil that was on the car when I got it had a cracked case with oil everywhere (except in the case).

Quickstep - Which model Pertronix coil did you use?

I bought the 40,000 volt 3 ohm shown in the link below.

I tried a bunch of stuff that day, so it's kind of fuzzy, but as I recall, the car ran with the Pertronix coil and the conventional points, but didn't run after I put in the Pertronix points. Here's the link to the Pertronix coil.

Pelican Parts - Product Information: PEL-PT40511