Capacitor Discharge (CD) Ignition?

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Richard Sweet

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I'm considering replacing my points ignition system in my '65 Dodge 273 V8. I'm looking at what's available in electronic distributors & systems. I've seen CD systems mentioned but don't know what they are or which one are considered CD's. What do they include and how do they work? I've heard that they work well.
Thanks, Richard Sweet
 
What's the rest of your build? 2barrel or Charger/Commando?
 
I ran a cdi many years ago.
If i had a choice,electronic all the way. The cdi system i had still used the existing point ignition,so dependability was still no better than points. Electronic ignition to me is a simple system.
 
CDI is the most powerful system out there, and MSD has parlayed it into an extremely useful builder-system, in the racing world.
But for a streeter,IMO,at up to ~1.2 hp/cid,there is nothing wrong with a Kettering Ignition System electronically triggered. And I prefer a magnetic pick-up myself.
Your ignition coil is already correct.If you want to upgrade your coil, I have had excellent results with the Accell Square top SuperCoil. It's pricey, but it will likely be the last coil you will ever buy.
So; all you need is a pick-up and the amp/translator to run it.
Unfortunately that usually means a new distributor with the proper guts in it,and the translator is commonly called an ECU. You can snag these used as they are known to work over a half a million miles. Or you can buy a Kit that includes the wiring you will need.
The magnetic trigger eliminates the points and their associated limitations and maintenance schedule. And that is all it does.
But I gotta tell ya; " if your current ignition lights all of the cylinders all of the time, nothing can be gained by switching to another type of ignition." quote from Smokey Yunich.
"Type"; in this context is referring to Kettering vs CDI.
 
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If you have a stocker and don't want to hassle with points, Pertronix is a good choice.
 
Advantage of the stock distributor, esp. if a 4 bbl equiped 273, is the timing curve.

CD ignition advantage is if trying to run larger spark gaps or other situations where higher voltage is needed. The actual voltage needed to cause a spark to jump across the gap in the spark plug depends on the gap and cylinder conditions at that moment. If it sparks at 10,000 Volts, then it doesn't matter if the system can only produce 15 kV. Multi spark is helpful in preventing misfires - more prevelant in 'hot cammed' engines with exhaust dilution at low rpm. Another reason for multi spark is the coil and CD ignitions are usually optimized for high rpm, and multi-strike is used at lower rpms.

Inductive ignitions tend to have longer spark duration than CD. That's not a bad thing on today's pump fuel.
 
Accell Square top SuperCoil.
Mine leaked oil. :(
Was running it with a chrome box, and I can't remember now if it went before or after the chrome box. I'd have to dig out my log notes. The windings were still intact, so it didn't die, it was just seeping. Smelled it first.
 
Mine leaked oil. :(
Was running it with a chrome box, and I can't remember now if it went before or after the chrome box. I'd have to dig out my log notes. The windings were still intact, so it didn't die, it was just seeping. Smelled it first.
IIRC the instructions were to mount it on it's side, which is what I did, in about 2004, on the apron, with a really long coil-wire,lol. Yeah it's ugly, but if someone comes to steal it, he better bring a long wire.
 
Something that seems to have been ignored::

MOST factory ignitons work somewhat like old breaker points, except the electronics turns the coil on and off rather than the points.

GM HEI is a bit different but it is still, in the end, "a switch."

Kettering, loosely, covers breaker points and the above

CD means "capacitive discharge" and it works sorto' like a photo flash. A high voltage power supply (inverter) charges up a relatively large condenser/ capacitor, and the spark trigger discharges that cap across the ignition coil.

CD does NOT have DC current through the coil like the previous units. MSD stands for "multiple spark discharge" (at some operating RPM)

There is some opinion, that in certain conditions, the very "sharp" spike of a conventional CDI may not fire fouled plugs, where, the broader, more powerful HEI spike might. In other words voltage along might not be the only thing.

Many of us here use a GM HEI module. When my car was together, the HEI even fired a factory Mopar coil.

Pertronix is not CD. It is similar to Kettering. Many like them. Only downside I see to them is parts. If it dies, you better keep spares in the glove box, as most parts stores don't carry them.
 
I have a CDI box used for firing the electric turnout motors on the turnouts on my model railroad. 25V out to the turnout insures a loud and decisive "SNAP" and assures the turnout is thrown in the proper direction, all but eliminating derailments due to an improperly thrown turnout. Works very well, but it'll knock the **** outta you in the right circumstances.
 
I used a Summit Racing 850027 distributor with a MSD 6AL (#6425) in the 318 block used to build my 392 stroker. The MSD distributors are much more expensive so I am happy with my decision.
FYI, I originally had acquired a MSD Stacker 7000 box long before getting the distributor but that was a mismatch. This box would work with your stock ignition and support any tachometer you might already have. Send a PM if interested.
 
I'm considering replacing my points ignition system in my '65 Dodge 273 V8. I'm looking at what's available in electronic distributors & systems. I've seen CD systems mentioned but don't know what they are or which one are considered CD's. What do they include and how do they work? I've heard that they work well.
Thanks, Richard Sweet

Don’t listen to anybody here except tool junky, mattex, rusty rat rod and 67dart273.
FWIW, Claudius is is a good fella! He gets a thumbs up from me.
Talk with him

Now on to the subject at hand and my personal experiences with the MSD brand. When I swapped in the box alone it did all they claimed. The addition of there coil helped a bit more since it was a better more power unit than stock. I used a electronic distributor. The MSD bid can be run with the points distributor. Not a problem. IDK about your coil though. I’d up graded it in a flash.
 
Run a analog ,non digital old school MSD box .It works ,can be touchy on installation.
Agreement with Rusty Rat Rod ,and 67 Dart 273... who actually explains the last century of ignition.
Think all three , out ....if you're a hot rodder ,study all three... (points ,HEI and Capacitive Discharge, and digital boxes ,as a fourth option).
To be honest, a Pertronix...fits a stock distributor. ..
The HEI option, fits a stock points distributor:
designedtodrive..gmail.com...
Have one ,on the shelf....
 
So what about tunability? An easy to tune system would have a big advantage. Which is the easiest to get a good tune with?
 
Which ignition system is easiest to get a good tune on?

That shouldn’t matter an iota. If it does, take it to someone who can tune an old school ride. Watch, ask questions, learn, DIY next time.

A multiple spark system will run best all things being equal.
 
I'm considering replacing my points ignition system in my '65 Dodge 273 V8. I'm looking at what's available in electronic distributors & systems. I've seen CD systems mentioned but don't know what they are or which one are considered CD's. What do they include and how do they work? I've heard that they work well.
Thanks, Richard Sweet

Hi Richard,
Unless you are having trouble firing oil fouled plugs I think a Magnetic discharge (Kettering Ignition) will deliver more enegy to fire the plugs. The energy storage capacity of a CDI setup is limited by the charge time of the capacitor. In most cases a 1 - 2uF capacitor is the max that will work. For a comparison of the two have a look at the magnetic vs capacitive discharge ignition article on this page:
Home
A really nice HEI electronic ignition setup can be put together using OEM replacement parts or junkyard parts by following this guide from the Slant Six dot org site. Of course you will need a mopar V8 electronic ignition distributor instead of the slant six part:
HEI Electronic Ignition Retrofit How-To - Slant Six Forum
If you want to keep your original points setup, you can trigger a Ford TFI module and coil as shown in this article over on the HAMB:
TFI using points how to
The MSD CDI products work well and have a proven track record, but I think an HEI or TFI setup has a slight edge on a stock or mild street engine and certainly has the cost advantage.

Good luck,
Scott McAuley
 
What else you got up your sleeve,lol?
Make sure you charging system is working well and use an electronic voltage regulator. Electronic ignition does not like low voltage and may result in module failure with 4-pin HEI modules. The 7 and 8-pin HEI modules are more tolerant of low voltage. Resistor plugs and wires are also a good idea.

Scott.
 
The GM 8-pin HEI is simplest and best. It was in 1985-95 V-8 trucks. Grab the module (inside distributor), connector & wire to pickup, coil & cable to it, and cut the red & wht supply wires as long as you can. TrailBeast here sells as a kit. You can leave the 6-pin connector open, or use it for spark timing control (from Holley Commander 950 or such). The Megasquirt site has more info. A Mopar distributor pickup can trigger it, but you need the polarity right for most stable spark.
 
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