Basic question on ignition coils. HELP

Hi ignition experts, I have a 51 Plymouth flathead with all the state of the art speed equipment and techniques of 1950s. I have amassed a cool collection of 50s and 60s 6 volt coils and am always looking for more! I am sure they all look better than they function............HOWEVER, on race day (theoretically of course) "Which coil should I use this year to improve my 1/4 mile time is the (crazy) question I ask myself.

Seriously, it would be a great learning event if someone could describe the process, tools and techniques required to measure which coil should perform best on race day.

Currently. I apply eeeny meeny minny mos method. Help!

Thanks all, Mike.


ps it would be helpful to descibe the use of an ociliscope if that is necessary, but even more helpful to discuss use voltmeter or other more reasonably priced tools as compared to osiliscopes.

 

Check resistance/ohms across the primary, - & + terminals, and the same across the secondary, which would be either of the - or + terminals to the center terminal. Here is a handy ink. http://autorepair.about.com/od/troubleshooting/ss/coil-test-ohm.htm

It doens't show any specs but you should be fine using the specs from your manual, they should all be about the same. Don't get fooled by the 50,ooo volt coil, you'll NEVER need that much voltage under any normal circumstances.

 

Using the wrong resistance coil will definitely hurt, but the coil itself isn't going to make more power UNLESS you are running some crazy boost/fuel combo.

What gives you hotter spark is longer coil saturation time, which is tough to get with points ign. Your 6 cyl will be better about that than a V8, simply because the coil isn't discharging as often. Set your dwell at the high end of the factory range, and make sure you have actual battery voltage at coil +. That's about all you can do...

 

Thx guys for the reponses. So, what can be determined from the measurements above? Do such measurements help determine which coil is working best or putting out more voltage or otherwise helping to determine what coil is best or preferable over other available coils. Is the high voltage measureable on a normal duty voltage meter? Do these measurements help identify a bad coil?......ie no resistance or very low voltage output. I love this stuff but question remains if its objectively measurable as to whether one hot rod coil is preferable to another.

Thanks for any help on this matter. (fyi I am looking for some practical reading on the matter to help educate myself on this stuff too....... Just thought others might be wondering about this issue too!)

Happy motoring, Mike

 

The coil will only put out as much voltage as it takes to fire the spark plug. Any spark plug, under any conditions. If the coil is capable of 25000 volts, but it only takes 6000 to fire the plug, it puts out 6000...if the next cylinder takes 8000, the coil puts out 8000, and so on.

That's why I said one coil won't make more power than another. Each one will only do what is required and no more.

 

Sorry if that wasn't the answer you were looking for...

 

exwestracer is talking about the difference between required voltage and potential voltage. Seeing this on a scope is easy, pulling a plug wire spikes the voltage to the max which is your potential... Required voltage is what you need to fire your plugs. Keeping your plugs and points and ignition system in good shape keeps your voltage needs low, reducing the work your coil has to do. That being said... if your coil bench checks ok, as long as you don't have other issues, you should be fine running any coil that checks out.

 

Wow, here I am looking for books and videos and asking questions about ignition systems and you all have described these concepts in only a few paragraphs. Thx for your thoughts.

Follow up question:

If the coil will rise to the ocassion to make a spark, then doesn't a coil need to work harder to fire a given spark plug with a wider plug gap as compared to another plug with a narrower gap. That is, if the gap is wider the coil will produce higher volts and or current to fire the plug. If this is the case, is there any benefit to running the widest plug gap that the coil will handle as long as the car still runs strong at the top end.?

Is a physically larger coil better....ie Why also would some coils be physically larger than others for the same engine and by the same coil manufacturer. For example some manufacturers made a larger coil for truck buses with the same engine as a passenger car. These coils were dubbed heavy duty. What are the benefits of a heavy duty coil. Wouldn't they make more power at the plug to ignite more fuel in combustion chamber.........this is what the mfg would say and this is what I would think before reading the above threads. So why what does a heavy duty coil do and would it be better to run one at the drags? Why is the heavy duty coil bigger?

You can probably tell that I still want to believe that some of my cool vintage 6 volt coils I have to choose from are better than others I have for top end performance on drag races day are better than others, especially if I put some higher octane fuel in the engine and widen the spark plug gaps. I am starting to think I am way off base and have been reading 1950s JC whitney catalogs too much.

Just trying to apply what I am learning so I can narrow the gap between my 51 Plymouth 6 and the hudson and Chevy inline 6s in front of me at the 1/4 mile drags!

Thx for any insight. Mike

 

Yes smaller gap requires less voltage to fire.
Back in the day we gapped our race plugs tight to help eliminate misfires at high RPM.. we also gapped our points to increase dwell time ... ah those were the days.. lol

 

Trucks and buses load the engine harder and longer than most passenger cars. The more load on the engine (rich mixture), the harder it is for the plug to fire; so the more voltage the coil has to produce. Couple that with extended periods at high load, and the coil tends to overheat. "Heavy duty" coils had larger internal wiring and more oil capacity to make them more durable, but they still didn't produce any more power....

As far as wide gapping plugs, it's been proven over many (100+ years) that .050 is about the biggest gap that makes any practical improvment in burn time.

There are many other ways to increase power in the engine, all the coil has to do is keep up...

 

If i were you I,d pick the fastest looking one and the other racers will worry,and blow a shift,and you will win.

 

I had a similar problem a while back. So I took an old Chev distributor, clamped it in a vise, and spun it with a grinder that had a wire wheel on it.

Then I tested each coil to see how long a spark it would throw and how bright it looked.

Not to keep you in suspense.. the winner was a stock coil and ignition module off an early 90s Ford, the Ford thick film ignition and coil. I installed it on a 1975 Porsche 911, it is about 10 times as hot as the stock Porsche ignition for 1/10 the cost.

Go ahead and test your coils and see which one throws the best spark.

 

Follow up question:

If the coil will rise to the ocassion to make a spark, then doesn't a coil need to work harder to fire a given spark plug with a wider plug gap as compared to another plug with a narrower gap. That is, if the gap is wider the coil will produce higher volts and or current to fire the plug. If this is the case, is there any benefit to running the widest plug gap that the coil will handle as long as the car still runs strong at the top end.?

Yes a wider gap makes the coil work harder with higher output> However if the wider gap isnt needed ( takes more time with wider gap) it is wasted energy with increased wear and tear on the parts . Typically wider gaps are used (longer spark duration) with leaner burning emission vehicles.

Is a physically larger coil better....ie Why also would some coils be physically larger than others for the same engine and by the same coil manufacturer. For example some manufacturers made a larger coil for truck buses with the same engine as a passenger car. These coils were dubbed heavy duty. What are the benefits of a heavy duty coil. Wouldn't they make more power at the plug to ignite more fuel in combustion chamber.........this is what the mfg would say and this is what I would think before reading the above threads. So why what does a heavy duty coil do and would it be better to run one at the drags? Why is the heavy duty coil bigger?

The only advantage to a heavy duty coil is to allow the coil to run and operate cooler.
Todays cars with COP (coil on plug) will use 2-5,000 volts and operate for hundreds of thousands of miles.



You can probably tell that I still want to believe that some of my cool vintage 6 volt coils I have to choose from are better than others I have for top end performance on drag races day are better than others, especially if I put some higher octane fuel in the engine and widen the spark plug gaps. I am starting to think I am way off base and have been reading 1950s JC whitney catalogs too much.

Correct your coils are very much different ! Different windings, different turns ratio (primary to secondary), and actually winding location ( primary inside the secondary vs secondary inside the primary)
I guess you could hook all these to a test circuit (using the distributor you are using to control the firing) and look at the scope waveforms from unit to unit.
If you lived in my neighborhood you could come by the shop and experiment..

Just trying to apply what I am learning so I can narrow the gap between my 51 Plymouth 6 and the hudson and Chevy inline 6s in front of me at the 1/4 mile drags!


The drags would be a good test track, change coils and run each and see what happens....I would suggest finding the ignition manual written by a Dr Jacobson and start studying, he did testing with a car driving down the road...
Thx for any insight. Mike[/QUOTE]