Technical Adding CDI to Points Ignition

Oops, missed that, thanks.

 

I'm running MSD CDI in my avatar, with an OT distributor. The voltage they produce is incredible. Over the years I've had a few ignition systems make me do the Scintilla Shuffle... never much fun, but you get over it with a few choice latin phrases.

Getting a belt from the CDI is something else. I broke down mid-trip at one stage, and had the Youngest Child crank the engine over while I held a plug lead near the block. The CDI felt I was a better earth, and gave me one hell of a boot. I unintentionally threw the allan key I had in the other hand, and damn near ended up on my ass. Took the Youngest Child a good few minutes to stop laughing.

Had a problem early-on where it would arc out and blow holes in the dizzy rotor. Turned out that one of my home-made plug leads was high resistance. Car ran fine, no miss, but at some stage the CDI felt it was easier to earth through the plastic of the rotor than through the high-resistance #1 lead. Remade the lead, and solved the problem.

Cheers,
Harv

 

Chrysler modules are like GM 4 pins you get what you pay for.

 

How about just going with a pertronix pointless Set up ?

 

Connecting the wires to them is a bit different, though.

 

@blowby

You can also use a GM HEI 4 pin module.

The problem is the HEI is triggered when the points close, whereas Points ignition [and TFI] are triggered with the points opening

This causes rotor phasing issues, but this can be easily remedied with a simple transistor in the wiring
[circled in red]



Figure 2 shows how to connect a 6 pole DPDT switch and still keep the condenser.
If you ever have a module failure, you can switch it back over to points / condenser ignition

 

Is the extended coil saturation time of a dual point still relevant with a CDI?

 

No.

Also, this is the HAMB, so if you use a CDI, be sure to find an old one, and be prepared for it to not work....

 

Good idea, I should at least carry spares. I'll look at Turlock in a couple weeks, might be some there. You don't go to Turlock do you?

I try not to mention it much, but having a wheelchair bound passenger adds a whole new dimension to breaking down on the road.

 

then stay away from that electronic crap!

 

Well that's what interests me in a CDI. If it craps out you just put the point wire back on the coil. Or even have it on a switch.

 

The major advantage of CDI is that the capacitor can be fully charged in a very short time [approx 1 millisecond]. So the CDI is suited to a high RPM application where insufficient dwell time is available.

The short spark duration is not good for igniting relatively lean mixtures in high vacuum cruising situations. To solve this issue many CDI ignitions release multiple sparks at low engine speeds.

GM went the opposite with the HEI which stretches the dwell time as RPM increases.

This can easily be achieved with a DPDT switch [I posted a schematic earlier], But you can easily wire it to switch over to another HEI or TPI module as well.

Points ignition is relatively simple and reliable. Points are simply a mechanical switch [every switch in your vehicle has contact points]
All a CDI conversion does is replace the condenser [also called a capacitor] with an amplified capacitor.
CDI's need a healthy charging system.

 

Yep, MSDs only multi spark to 3,000 rpm. And use .9 amp per 1,000 rpm.

 

Don't let that .9 amp per 1,000 rpm. fool you!
Everytime you double the volts ,you halve the amps so the energy remains the same [except for heat losses]
This was the marketing bullshit years ago when the hot ticket was a 90,000 volt coil [or whatever]
I've seen this as the cure-all on HEI ignitions which were limited to 5500 rpm. And higher voltage coils made them worse!

Sparks require energy....as in Joules [not just volts]
A coil is just a transformer, so the best way to get more out of it is to put more in [that's the story of life as well]
Most CDI's, TFI's, and HEI's work on that principle . So the perform better with a good charging system.[because they need an external source of power to perform the wizardry]

I prefer the HEI because it provides a big fat wet spark at low RPM , and as the revs climb it stretches the dwell [because there is less time/milliseconds at higher RPM]

 

@blowby

Paul,
Here's a bit of reading about condenser failure [and the $3 solution] for the good ol' bulletproof points ignition
http://nonlintec.com/sprite/cap_failure/

 

The recent consensus on the British car forums is to just keep the old condenser in there....

 

"Back in the day" good mechanics didn't necessarily swap out the ignition condenser routinely as part of a Tune-Up, this can be difficult to explain to the customer, who might not understand why, and after all he is paying for new parts.

But if the points are wearing evenly there is no benefit to replacing it as such. These days it is practically a foolish thing to do, and the parts stores are practically complicit.

 

That's if you can get a decent one [not made from "Chinesium"]
When we rebuilt the engine in our 57 Chevy, we had 3 condensors fail in a row [straight out of the box]

So we scavenged the old Delco condenser out of the trash and reinstalled it [it's been there ever since]

 

if some of you can use 4 speed auto OD transmissions and 5 speed transmissions, something like a reliable solid state capacitor should be just as acceptable…
GM HEI can draw 20 amps under certain conditions…The original applications had #10 feed wire

 

Hey don't confuse me with difficult math formulas. So at the 3k rpm you say an MSD is drawing more than 2.7A?

My '56 came to me with the internal condensers replaced by this elegantly mounted external one. Been on there since it was parked in 1974, and by looks of it a lot longer. I'm afraid to touch it.

 

That looks like a Mallory "trash can" condenser.

Show us the other end of the wire, and inside the distributor....please?

 

There's pic in post 28 on page 1. The big black wire goes to it, the green to the coil.

 

thanks, I missed that.

If the wire connection at the condenser looks ok (hard to tell from the picture?) then just leave it alone. Or get an NOS Delco condenser or two from ebay, and either take it with you, or install one now and take the other along. And leave the trash can there, and keep the wire, just in case you need to get it going again. But that's unlikely.

 

Getting this condensor tester running is on my (long) to-do list. Suspect the "specially calibrated leads" are long gone. It tests at 500V DC, which makes me suspect that at some stage I will end up looking like Beaker from the Muppets when I pull it apart. Need to think through how I turn my 12V battery charger into a 6V power source too.




Cheers,
Harv

 

One problem with using a capacitor tester on ignition condensers, at least modern condensers, is that the failure mode is usually something that the test won't detect. It's usually intermittent, and caused by varying internal resistance, where the film assembly meets the metal housing, or the contact terminal at the other end. But if the condenser is really really bad, the tester will find the problem.

 

I bought a case or 2 of new old stock TIGER cdi ignition boxes . Ive been using 2 on different cars for over 15 yrs . No complaints.