I know this has been covered before and I have researched it, but my question isn't typical. I started a thread https://www.corvetteforum.com/forums...i-missing.html a while back when my car wouldn't start and it turned out to be a bad coil. I ordered a new one from a vendor, but when I got it, I checked the resistance and it was 2.1. All the research I did here on the forum and other online sites said it should be 1.5-1.7, so I sent it back. The vendor is one of our supporters and was great to deal with and called me a few times. They contacted the manufacturer and were told they are making them at 2.0-2.1. What are your thought on this?

 

What does Pertronix say about the coil resistance?? Have you contacted them?? Is it one of their coils??
If they bless it and don't void you warrantee on the electronic pickup, I would use it.

 

DC resistance is different than inductance.

I agree with R66 - use the coil that the manufacturer (Pertronix, I see in the other thread) recommends.

 

I've had the pertronix installed about 16 years and have always used the stock Delco 202 coil. I bought a flamethrower years ago, but based on feedback from this forum and all the problems members have had with it, I never put it in my car. No, I have not spoken to pertronix and don't see the need.
My question has to do with the current Delco coil manufacturer claiming that 2.1-2.2 resistance is how they build them. The one I bought, bench tested and sent back (without testing in my car) is now on its way back to me. After speaking with the vendor, I agreed to have them send it back to me and I will test it in the car. I will post the results.

 

Ok, got the 202 coil back from the vendor (Zip) and bench tested it and resistance was 2.1 as the manufacturer told Zip is how they are building them. I started up my car with the older, but known to be good coil (1.6) and warmed it up. I then switched to the new coil and it started up and ran without any problems.

So, I guess the old numbers of 1.5-1.7 resistance doesn't necessarily apply in all cases.

I am by no means an electrical engineer, so I have no idea why one works at 2.1 and another one won't.

I will keep the older coil in the vehicle just in case.

 

Although I took a TV repair course back in the transistor ages, I am not an electrical expert. I do know that increased resistance does affect the output voltage and amperage.

A minor change in resistance can make major changes in performance in an electrical circuit. I don't believe it will be a major change in a basic electrical pickup as it only performs a switching function like the old transistors.

However, the electronic pickup in your distributor may actually respond better with the higher secondary resistance on the coil. As I recall, GM installed and recommended less coil resistance for the TI (transistor ignition) than the points distributors. But, the TI ignition had an amplifier for the spark and that may have very well been the reason for the reduced coil resistance, not the pickup.

Either will work, the only questions I would have are:
1) are you getting optimum performance from your Pertronix with the 2.2 ohm coil and
2) will it affect the life of the pickup???
Those are questions I would only accept the answer from the manufacturer of your pickup.

As the old single coil technology dies, classic car owners have to accept some variations that are not necessarily compliant with the original design due to parts availability.

 

Pertronix I and II models were always a crap shoot and the company gave varying advice on coils and ballast resistors.... At one point they had some measurements cited on their tech page to determine proper coil resistance for a unit - those are gone now...

However, the Pertronix III Flamethrower coil specifically made for the Ignitor III has a primary resistance of 0.32 ohms. This unit is intended to be used WITHOUT a ballast resistor. Stock style coils of 1.7-2-2 ohms may work or may not.

With the bad rep of the Flamethrower coils I just use the MSD Blaster II 8202 coil with a primary resistance of 0.7 ohms. Just scrape off the label and paint it black.

If you have a high performance environment the MSD Blaster II 8222 "high-vibration" (more money) coil is already black and with 0.7 ohms primary resistance.

If you want to use stock components WITH original spark plug wires, WITH ballast resistor and WITH an original coil use the Lectric Limited Breakerless SE conversion instead of the Pertronix.

I can't make it simpler than that...

 

You can make coil testing a large science project in a short time Mr. W. Unless you own a oscilloscope and high attenuation probes your not going to be familiar with using one and a steep learning curve is waiting for you.

All design engineering specifications for a coil are kinda esoteric to the novice as I consider then more of a inductor than a transformer and we all have a difficult job with the dynamics of supplying spark current. They only have so much energy to supply for each spark which means the amount of that energy used to jump the gap and start the spark is no longer available to supply current to maintain the spark. The spark still needs energy to get the burn started once the spark jumps the gap but this is only what's left of the total energy from the coil field collapsing and if it can't start the burn you gotta dud. That's why plug gaps are so important as are compression pressure and fuel mixture (as lean mix is harder to start burning).

OK enough of my eblaborating and I hope I didn't confuse you. But I think you are doing the right moves by contacting the mfr and using the experience here on the forum for what really does work.

Congrats and thx for the feedback!

 

Some years ago I ran into this with new AC Delco HEI coils. I returned 6 of them before I got an older one that ohm'd out in specs.

 

I guess they are being manufactured differently now and 2.1 is now "within specs" and works fine. My older one quit working and was 2.4, another old one I had on the shelf was 1.6 (and worked) and now the new one at 2.1 (also worked). All are Delco Remy 202s.

I've run the same older Pertronix I, ballast resistor and 202 coil for the past 15 years on my basically stock L79 engine without any problems until the aforementioned coil went bad.

As always, I really appreciate all the valuable feedback and advice I received on both my threads

 

Please understand that what coil "works" at idle or cruise, does not say a coil will "work" properly at high load @ high rpm, when the coil is at full (hot) temperature, which is the worst case condition.

Idle is the "easiest" on the coil, where dwell time is at it's maximum (not dwell angle, but the actual length of time that the points are closed for the coil receiving full current). This includes electronic points replacements, where the dwell angle is "fixed" at one dwell angle.

Full load / high rpm is the worst condition for the coil to maintain sufficient energy to jump the gap. And as the coil becomes hotter, coil resistance increases, decreasing current and resulting output. As load increases, actual cylinder compression increases, which requires a higher spark energy to jump the gap. As RPM increases, actual dwell time decreases.

Also, one of the potential benefits to using a points replacement module, is the possibility that it was designed to carry higher coil currents. If it was designed with that in mind, then using a lower resistance (and therefore a higher current) coil should increase coil output energy. In other words, if the points replacement module company recommends a different coil, it might be advantageous to find out "why".

Many other factors go into coil design, primary & secondary resistance, coil turn ratios, etc., but for actual road testing, the above should be a starting point.

Plasticman

 

And that is why I will carry a known good coil in the car at least until I'm convinced this new one will work under all the conditions you stated above. Thanks