I'm looking to put an HEI in my 71. I'm new to working with cars and this will be my first project of any significance. I've read all the forum posts I can find, but don't see anything about this:



It's mounted close to the firewall on the passenger side of my wiper motor. The wires lead to the distributor, coil, and carburetor (Edelbrock Performer elec. choke).

The writing reads:
CP-50B DALE
.8 ohm 10% 9824

Is this just a resistor?

Thanks.

 

Thats the ballast resistor for the coil on your ignition. It limits the electrical current fed to the coil to keep it from burning up

 

Thanks much!

 

Welcome

 

I'm guessing the wires to the coil and choke connect on the right and the distributor is the one on the left? Looks to me like the resistor for your points. It's purpose is the limit voltage to the points after cranking to make them live longer.
Hope this helps,
Jeff

EDIT:
Wasn't trying to argue, SIX posted while I was typing my response.

 

It's a ballast resistor alright, but my question is what's it doing in a 71? 1967 was the last year GM used a resistor. Obviously it was added by a previous owner, but I wonder why.

 

It limits the current, not the voltage.

 

Wonder what happened to the original resistor wire?

 

Maybe there was a Pertronix in it at one time (requires no ballast) and a PO pulled the resistor wire. Who knows why these cars are put together like they are [after 40 years of 'Bubba']?

 

but if you are installing an HEI you will not need it.

 

 

OK awesome thank you. That was going to be my next question.

 

A resistor reduces both. Aren't you an EE? WTF, you should know better than that.

 

I'm not only a EE, but an ignition and ECM/PCM designer. In the real world! I don't just play one on TV or on car forums.

The poster said the (ballast) resistor's purpose was to limit the voltage to the points. That is wrong! Anybody that states that is wrong, including you Turdle. The points are subjected to 12 volts between every dwell period. Every one! Additionally, if 12 volts was such a scary thing, how would the points survive the several hundred volts they see at the end of every dwell period? (I know the answer, but I don't feel like typing it all out.)

The ballast resistor's sole purpose is to limit the peak primary current. Additionally, the voltage at the points during dwell is ZERO, whether there's a ballast in the system or not. You're a EE too, so I assume you have a 'scope at home where you can verify this yourself.

If you have some concerns about my proficiency regarding ignition design and operation, I'm happy to discuss the formulas we use for calculating the coil primary current, risetime, energy storage, and the resulting voltage drop across the ballast (in antique systems) due to current flow if you wish. Remember, to get a voltage drop there has to be a higher "rail" voltage to begin with. In the case of the points and coil, that rail voltage is 12.

I'm tired of typing.

 

yea... he's right, sometimes you can misinterpret things, we had a go-around about this before and I misinterpreted 69427 (still want to know what the number stands for) but yes it is used to limit current, and it does that by making a voltage divider, so yes you will see a lower voltage on the demand side of the resistor when the points are closed. hope that clears it up a bit.... and im an EE also

 

Car in background ('69), and current street/track engine being used to mockup my replacement run-in/break-in stand. (I sold my previous stand when I moved a couple years ago, and apparently the guy likes it 'cuz he won't sell it back to me now that I need one again.)



New track engine (under construction). Hoping to get it into the car later this month.

 

very very nice this one.... wow... i would love to build a 427.....

 

The resistor is there so you won't overheat the points or rundown the battery if the ignition key is left on and they happen to be closed. Electronic ignitions provide a rising edge trigger so they are not a concern. I would think that it could be taken out and full voltage applied as a no cost performance boost. That would allow the coil to charge quicker and provide a hotter spark. Just don't leave the key in the run position for any length of time with the engine off.

Or am i full of crap?

 

That's beautiful !!!

 

On most things, that's a resounding Yes.

But, your last comment has merit. I've mentioned to previous posters that for drag race use it's possible to have a toggle switch wired between the fuse box and the coil + terminal. Switching out/bypassing the ballast resistor during high RPM situations allows the coil to charge much quicker, resulting in more coil/spark energy. (Of course, a toggle switch doesn't have the bling factor of a red machined aluminum box, though. )
Just remember to open the switch on the cool down drive back to the pits.