I recently rebuilt a big block for my 69, and its all installed and running, but I can never get the timing set right. When its running the best going down the road it starts to backfire through the carb, meaning the intake valve is open when it gets spark.
But my question is about my ballast resistor. I not exactly sure what the purpose of the ballast resistor is. I think what my problem is i am not getting enough voltage at the coil. If I don't have enough spark at the coil my timing will never be right. Should I have reduced voltage just during start, then 12V at the coil when the car is running? Another question, if I am running a new HEI distributor do I even have to have a ballast resistor? I know the engine is fine, ive had it on the dyno, and everything tuned right, i just think my wiring is off. Thanks

 

For a points dist, you run the resister for power and 12 volts just to start.

For a hei, you run the full 12 volts which usually means running a new wire from the fuse box to the dist. Hei can run from 9 to 15 volts.

If you are running a points dist make sure you are not running an external electronic coil.

 

No. Run a 12v switched wire(about 8-10 gauge) to the positive side of the distributor

 

Stock, there is a wire from the starter that supplies full 12V to the + side of the coil during startup, at the same point on the coil is a wire that runs through the ingnition switch and is hot (12V) when cranking and in run, the other is only hot during cranking. This is ok because the same battery is used, so when you release the key, the V drops to the resisted V, they say 6-8 volts, that coils need to run safely. Mine is a '73, and by this time, they used a Resistance wire that starts at the firewall connector and runs to the coil (inside the cab, it's just a normal wire into the cab side to the connector).

Yours may have a Ballast resistor in place of the R-wire, with normal wire running to it and away from it. Either of them need to be in, if your running a coil. I would suggest switching to an HEI, but remember DO NOT USE a ballast reisistor or the reisitance wire if your running a HEI. If you do switch to an HEI, use a 8 or 10 gauge wire, like stated above, from the ING tab in the fuse box and run it to the BATT hook up on the HEI, direct. it will need to be hot in both cranking and run, which the IGN is, IGN is printed on the fuse box right below the male slider type tab, crimp a yellow (for the gauge) silder type conn onto the pass side of the wire, run it into the engine bay(there was a swall plug above the fuse box on my '73) and over to the HEI and crimp the other end. that simple. ofcoarse you would have to buy a Tach drive HEI or run an after market tach, or switch your tach to a 75 or later one, but you can't beat an HEI for good spark, price, ease of use and reliability. If your not crazy NCRS, i would highly recomend the swap, and remember to disconnect the vac to the Dist and plug it, when setting the timing, in case your a real junior . Good luck,, Chris

 

If you're running points, you need a ballast resistance in the primary circuit to keep from burning up the points, and possibly the coil. The ballast resistor limits current, it does NOT regulate voltage. (The system runs off twelve to fourteen volts, no matter what you might hear.) The HEI distributor does not need a ballast reistance in the wiring as the primary circuit current limiting is done (very efficiently) in the module, not in an external resistance.

 

Ok thanks alot. Ill just run the wire from the fuse box to the coil. Another question, with that one wire will that give me 12v during cranking and run, or do i have to run the wire from the starter to the coil too. Yeah it cost me but i had a hei made with the tach drive on it, so thats not a problem. Thanks guys, it all makes sense, i just didnt know if i needed the ballast resistor. But now i do.

 

Well I hope you didn't pay over 200 for it, because they are widely available for about that much. You will no longer need the 12V wire from the starter with an HEI. (Just a tip, you can go to a wrecking yard and walk around till you find a car with an HEI unit in it, and cut off the "batt" clip into it, about 3", then, with the 10 gauge wire you run, get a Yellow butt spilce and strip back about 3/8in from your wire and the HEI clip and set up the end. If you don't want to do this, you can make a Yellow female lug end crimped on fit too). You will just need the the wire, 10 gauge with a yellow female lug crimped onto it, pluged into IGN tab in your fuse box to the BATT lug on the HEI. That's it. HEIs are great. No resistance wire, no ballast resistor.