I'm preparing to mount my rebuilt 350 onto the restored chassis while the body is still off. I want to be able to run the engine once that's done, but don't won't to install the new electrical harness yet. I know my car used a resistance wire from the ignition switch run position to power the coil at a reduced voltage after starting with full voltage to the coil provided by another regular wire from the solenoid to the coil. Without that resistance wire, I'll use an external resistor in its place for my purpose. I haven't been able to confirm the actual resistance the factory wire provided, but I have seen references to 1.35 ohms total or 0.5 ohms per foot. Searching on line, I found that Standard Motor Products RU-11 ballast resistor is listed as compatible with 1957-63 Corvette 283 and 327 engines (before Chevy started using the resistance wire) . That resistor is rated at 0.5-0.6 ohms cold and 1.75 ohms at operation temperature. My original resistance wire just has "Resistance - Do Not Cut" printed on it without any actual rating and wiring diagrams I have just show the resistor, not an actual rating either. The factory resistance wire is about 3-2/3 feet long, so if the 0.5 ohms/ft is correct, then 1.75 ohms total should put me in the ball park.

Do you think the RU-11 will work for my temporary set-up for the 1971 350 engine?

Thanks for any help...

 

The ballast isn't there to lower the voltage, it's to limit the current. For low load/RPM operation any reasonable ballast (.5 -1.5 ohms) you have should be sufficient to limit the current. Additionally you can also reduce the dwell angle to help reduce the average current that the primary circuit is switching.

 

1967 Corvette points ignition resistor, 1.82 ohms
https://www.napaonline.com/en/p/ECHICR13

 

nwav8tor
If I was you I'd just use the "best-guess" ballast resistor..... worse comes to worse you replace a set of points. I wouldn't even ponder it that much. If you're really curious you could take an ohmmeter reading on the old resistance wire.

 

I already had checked the new Lectric Limited resistor wire (cold) and got just a hair over 1 ohm on the meter. It was hard to read the pointer scale on the Rx1 setting, so I may have to find a digital meter and check it with that for more accuracy...

 

Tested the new coil resistor wire with a digital meter today and it read 1.7 ohms, so I'm pretty confident that the 1.75 ohm ballast resistor I bought should do the trick.

Thanks all!

 

You could buy a cheap VW or similar coil that has the resistor built in and doesn't need an external one.

JIM