Specs on Coils- 202 and 091?

[James B.]

I am curious on the voltage output of the original 202 and 091 coils and if the new repops (C Central and Paragon- GM authorized etc) meet the same specs or have been 'commonized'. I have a 64 fuelie that should have an 091 but just found it has been running for the last 10 years with a 202. I have a '67 L79 that could use the original 202 so thinking about buying a new 091 for the '64.
Also question ballast resistors. I see the 64 judging manual calls for one with a black dot. somewhere I read that in the fifties corvette had a 3 ohm resistor but in 1963 changed to 1.8 ohm. Not sure what the one on my car is because there is some primer spots on it. C Central's 'black dot' resistor is 2.0 ohms- maybe that 0.02 ohm makes no difference. I just want to make sure that the ballast resistor I use is compatible with the coil. Any help would be appreciated.

[Jack H.]

Re: Specs on Coils- 202 and 091?

That's 0.3 ohms for the ballast resistor used with the '091 coil--not 2 ohms...

Essentially the 'hot' ignition setup ('091 with 0.3 ohm ballast) was used on standard ignition Corvettes until mid to late 1963 when the 'cold' ignition setup ('087/'202 coil and 1.8 ohm ballast) was introduced for lower reving engines to extend point life and extend tune-up intervals. In '65, all non-TI equipped Corvettes adopted the 'cold' ignition setup.

Since your '64 FI engine had a high rev profile, it would have left the factory with the 'hot' ignition setup...

[Duke W.]

Re: Specs on Coils- 202 and 091?

Coil voltage, which is usually the open circuit voltage is a meaningless measurement. What counts is energy, and the higher the primary current the higher the secondary energy.

There's a slight difference in resistance specs of the two coils, but that doesn't say anything about inductance.

The 0.3 ohm/091 coil was tough on points due to the high primary current, which is why it was abandoned after 1964 on all Corvette engines.

To be on the safe side, it's probably best to run the higher resistance ballast with the 202 coil, since that's what it was designed to mate with.

Duke

[Jack H.]

Re: Specs on Coils- 202 and 091?

Excellent comments, Duke!

Primary and secondary winding resistance specs were intended for easy 'go/no-go' mechanic testing. To get at the real MEAT, the coil's native energy transfer profile, you have to measure inductance (few have RLC testers) AND understand/measure the magnetic permability characteristics of the transformer's core.

So, the common specs given are necessary but NOT sufficient to fully test/characterize the ignition system...