Points ignition output voltage and length?

[Charlie Cheap]

As the go-to-guy for first generation 6-cylinder Mustangs, I have an unusual question. With a carburetor type engine, operation at 1000 to 5000 rpm, is a modern electronic ignition truly better than a hot points system? After studying both types it seems newer ignitions make a hotter spark but much shorter than points. Probably the reason for MSD systems. It looks like a good hotter coil (ACCEL 42,000 volt) with a slightly lower ohms resistor to induce a small increase in primary voltage, would make plenty of secondary voltage to fire plugs with a slightly larger (from .030" to .038") gap. In my 1965 Mustang with a .060" overbore, 2-barrel carburetor, mild head work for ethanol, a cool-air intake, hotter points ignition and free-flowing exhaust, I see no gains in Horse Power, Torque or MPG with electronics. My points ignition is built to the max parts wise, using BWD Select (best available material), setup for street use. My wires are best available as are the double platinum spark plugs. How hot a spark can a good points system create, and how does it compare to HEI or later computer-controlled systems in the lower RPM range?

 

[anorlunda]

This article suggests that maintenance, rather than performance is the primary motivation for electronic ignition.

The disadvantage of the mechanical system is the use of breaker points to interrupt the low-voltage high-current through the primary winding of the coil; the points are subject to mechanical wear where they ride the cam to open and shut, as well as oxidation and burning at the contact surfaces from the constant sparking. They require regular adjustment to compensate for wear, and the opening of the contact breakers, which is responsible for spark timing, is subject to mechanical variations.

In addition, the spark voltage is also dependent on contact effectiveness, and poor sparking can lead to lower engine efficiency. A mechanical contact breaker system cannot control an average ignition current of more than about 3 A while still giving a reasonable service life, and this may limit the power of the spark and ultimate engine speed.

 

[Charlie Cheap]

During my research I found ignition parts for points have been improved over the years, and today's points, if one buys the best available, are much better than factory originals from the 1960's. The condenser (capacitor) is also better, if one buys the best available, and it definitely helps point life. Making sure the points faces are square to each other also helps. Mine last over 9,000 miles between replacement. That is 3 trips across the US, LA to Jacksonville. Anyone here know what secondary voltage a good points system can produce, and what difference in spark length there is?

 

[Charlie Cheap]

I am trying to find the maximum output voltage of my old but modified points ignition. As an old car builder, I think my points are able to produce a very good daily-drive (non-racing) spark without the need to change to a modern electronics system. Over many years I have used both on the street, and find no noticeable difference in Horse Power, Torque or MPG. Anyone have any ideas about the practical difference between the old and new?

 

[Gordianus]

[Moderator: This post and the following post were merged from a second thread started in EE]

I´m an old guy and I clearly remember point ignition (my old man had a Dodge Dart. I learned how to adjust them, how clean them with a very fine file, how to keep the points parallel to each other, etc, etc. A good set may last one year. Currently I own an Isuzu truck. I haven't touched the ignition system in 22 years. That's reliability.

 

[Ranger Mike]

[Moderator: This post and the previous post were merged from a second thread started in EE]

Stock 1965 points could jump a 0.030" spark plug gap. New CD ignition can shoot a spark 0.060" and over a very long dwell compared to the few degree crankshaft dwell of the old points. I would never swap out a point distributor for the new stuff. I have done it on race cars and on the current sports car race course we use the point fired distributor but with a conversion to eliminate the points and run a single 30000 volt coil. This is a super low electrical drag. The CD ignition is huge voltage hog. Throw and old set of points and condenser in the repair box and maybe an old rotor and drive it.

 

[Charlie Cheap]

Ranger Mike, I think we agree about old ignitions, and I am speaking about a modernized old points setup. Gentlemen, I graduated Elkins Institute the last work-day of 1969, and left the Radio-TV-Satellite business in 1988. So my memory of Ohms Law and related formulas is very lacking. With a 12 volt source, a 1.3 ohms ignition resistor, an ACCEL 42,000 volts coil with a 96 to 1 ratio and 1.4 ohms primary resistance, Dwell set at 38 to 40 degrees, the very best available parts (Rotor, Cap, Points, Condenser, Plug wires) and double platinum plugs gapped at .038", does anyone know what voltage the plugs will see? I understand dwell and plug gap change the circuit load, as well as type of wires and some other things. I am simply trying to show other Mustang owners, in my opinion on the street, electronic modern ignitions are not necessary for our 6-cylinder. Our points ignition, especially if updated with more modern parts, will produce a very good spark.

 

[Charlie Cheap]

After retiring I build just for me, but I still answer questions for the M6A group on-line. After decades building V8's I find the little 4 and 6 cylinder engines challenging. It looks like most who own first generation Mustangs feel the need to upgrade the ignition in the old Pony. I have been there and never found the so-called upgrades to gain anything in the real world.

I tried to post a picture of my 65 SIX engine...without success...I think?

 

[Tom.G]

Here is a thesis on the subject from the Naval Postgraduate School. http://www.dtic.mil/dtic/tr/fulltext/u2/742933.pdf
I've only spot-read the first dozen pages (of 83 total) but everything looks good and quite reasonable, some finer points may be overlooked but there is a lot of information there.

One possible drawback is it is over 45 years old, so the current batch of enthusiasts just might disregard it as being "too old to matter"! But heck, it's old technology, being investigated when CDIs were becoming available.

A spark-ignited engine needs a specific minimum energy in Joules (actually milli-Joules if I recall correctly) to ignite the fuel-air mixture. This of course varies with the engine operating conditions. As long as you have enough voltage to initiate a spark (10,000V - 15,000V) and enough energy to maintain it to dump the required energy, you are good to go. A few manufacturers of small engines used to make this information available.

As others have pointed out, CDI systems need less maintenance than the Kettering system. CDIs will perform better with fouled plugs because of the faster risetime of the spark voltage, less energy is lost to leakage through the fouling before the spark starts, leaving more energy available for fuel ignition. More factors are mentioned in the above article.

Cheers,
Tom

edit: fixed a typo

 

[Charlie Cheap]

After writing a very nice KUDOS post for the help received from you TECH guys, I hit the wrong button on my computer. Believe me, it is out there in some cloud looking for a place to go. It was well written and wonderful to behold. Anyway, thank you very much for the TECH help with my ignition question. With references to read and NOW, being able to write like I know what I am talking about, I will look like a professor rather than a shade-tree mechanic. Actually I am an ASE certified mechanic, but they do not go into deep discussion about the "whys and hows" of engine design like engineers. It is nice to know I now have a place to get that kind of answer when needed. Computers are here to stay, but just being old does not necessarily mean obsolete. My 65 has ZERO computers and no "code-reader" is needed to keep it running. With Halogen headlights/fog lights, front disc brakes, 15" radials, rear sway-bar, poly bushings, gas shocks, Monte Carlo Bar, Export Brace, GT springs, Lowered about 1", and roughly 40 more HP than when new, the little 206 ci SIX will drive a hole in the wind!

 

[Charlie Cheap]

Here is a thesis on the subject from the Naval Postgraduate School. http://www.dtic.mil/dtic/tr/fulltext/u2/742933.pdf
I've only spot-read the first dozen pages (of 83 total) but everything looks good and quite reasonable, some finer points may be overlooked but there is a lot of information there.

One possible drawback is it is over 45 years old, so the current batch of enthusiasts just might disregard it as being "too old to matter"! But heck, it's old technology, being investigated when CDIs were becoming available.

A spark-ignited engine needs a specific minimum energy in Joules (actually milli-Joules if I recall correctly) to ignite the fuel-air mixture. This of course varies with the engine operating conditions. As long as you have enough voltage to initiate a spark (10,000V - 15,000V) and enough energy to maintain it to dump the required energy, you are good to go. A few manufacturers of small engines used to make this information available.

As others have pointed out, CDI systems need less maintenance than the Kettering system. CDIs will perform better with fouled plugs because of the faster risetime of the spark voltage, less energy is lost to leakage through the fouling before the spark starts, leaving more energy available for fuel ignition. More factors are mentioned in the above article.

Cheers,
Tom

edit: fixed a typo

Tom, my understanding is, the CDI and other electronic ignitions make a bigger spark but a much shorter one. They also are a much bigger drain on the electrical system and far more complicated. No doubt they are better in the upper RPM range but show little if any benefit at normal driving speeds. YES, they will fire a fouled plug, but a car guy seldom let's plugs get fouled. The reason for them is no maintenance and they will continue to work when a points system would not. After 50 years driving cars I built with very good points systems, I NEVER was stranded beside the road due to points ignition. Actually, I can't remember the last time I was parked beside the road for any reason...other than helping someone.

 

[Ketch22]

After 50 years driving cars I built with very good points systems, I NEVER was stranded beside the road due to points ignition. Actually, I can't remember the last time I was parked beside the road for any reason...other than helping someone.

There is a peculiar form of truth to this. Electronic control units can provide much better engine control than older style engines. They are better at providing economy and performance. However there is a lot to be observed from the advantages of modern engines and the way they also have improved our experience.
When I started with tuning gas engines I was working on the new style V8 motors and getting amazing performance. I was also rebuilding old flat head Fords. Both of these were point ignition and both needed to be rebuilt at 100K miles plus/minus depending on how they were treated. I well remember 24 years later when a friend asked me to look at his car because it "was not running right." Turns out it was a straight six ford, it had 87,400 miles on it, and it was running on OEM oil, plugs, points, wires and filters. The man had never had his vehicle serviced, ugh.
When Cadillac introduced their NorthStar motor which only needed it's first TuneUp at 100K it was an amazing thing. However part of that was the longevity of the equipment, part was the duration of service. In retrospect I find it worth reflecting on, as the quote leads us, a car person (or a motor head) does not actually let their car get to that point and thus does not see an improvement from mechanical to electronic ignition. The performance improvements are from better internal design and control. Items such as multiple valves and better timing control, better oil and materials, and better control in machine work and fabrication are all part of the "modern improvements." These all add to longevity and performance. Before I changed direction in my engine work I was working on nitro racing engines. These are still old style ignitions. They are destroyed in approximately the first second of a 4 second run but still doing pretty good.
Just a brief reflection on a comment. The Original post asks how much better is electronic over mechanical (or at least it appears to be the root of the post). I would tend to agree that if you are going to stay with the old style motor, old style engine control, and old style air flow management there will be little observable gain in changing the ignition. Once you have ignited the mixture in that motor one is committed to the rest of the path as well. The explosion already happened and the gains have been achieved. A 0.4% gain for better ignition is negligible at the street driving level. Stay with what you work on and can support mechanically.

 

[Charlie Cheap]

Ketch22, thank you for your post referencing my question. Back in the late 60's I raced a 1940 Ford coupe with a corvette V8 and 4-speed. This was before electronic ignitions so our goal was to make points as good as possible. Remember SUN machines? We would modify our dizzy advance curve, with swing-weights, spring tension, vacuum chambers (I also drove the car on the street) and using the best parts available. Using the hottest coil we could find, and the lowest safe ohms input resistor for max output, and read our plugs after each run, we could workout the best combo. I am not an engineer but as I am sure you know, there are many at the track. Knowing I was going to work with cars all my life, I became a "Brain-Picker" and kept records of ignition timing, spark gap, points type, plug wire style/material, and brand of cap-rotor-condenser, to keep my homemade ignition working. Having both points and modern electronics ignitions in my daily driver cars, I never noticed any gain or difference, so I decided to get a technical answer from this site. I still have not heard what the maximum possible voltage at the plugs would be, but I'll try to find a "formula" to do that. THANKS again.

 

[anorlunda]

I still have not heard what the maximum possible voltage at the plugs would be

Why does that matter? Do you see a link between max voltage and performance?

 

[Charlie Cheap]

Ketch22, I forgot. I understand CNC machining can hold much tighter tolerances than previous machining methods, and modern lubricants help keep things moving and cool. Better head design, turbo chargers, variable-valve timing, computer controlled fuel-injection, and better materials make better engines with more power and economy. I am amazed at my wife's Escape's 96ci 4-cylinder making 170HP. One thing some ignore is today's points ignition old cars, use today's better materials/lubricants when rebuilding. I was shop superintendent for a city maintaining patrol cars, when 5w-20 oil first appeared. It was not available at the auto parts stores or the Ford dealers, so I had to call Ford. My Dad and brother were both machinists and I understood closer fitted moving parts needed better lubrication, so when building I keep things as close as possible, and run 5w-30.

 

[Charlie Cheap]

anorlunda, maximum voltage matters little to me, but the guys asking questions on the M6A site, where I am the Go-To Guy, seem to think it does. The reason for wanting to know is to answer their question...even if irrelevant! Classic Mustang 6-cylinder owners can't seem to get past ACCEL, Mallory, Pertronix, etc. HYPE! I love our capitalist system, but sometimes advertising overrules truth/facts...Totally Dude. Sorry, I drifted off into never-land. My 6 is modified to the max for the street, and I have a Pertronix triggered dizzy. A points change-over is in my trunk, just in case. I have tried to explain my 50 years of study, but some keep trying to get me to admit, the $500.00 plus they spent on their YOU CAN WELD WITH OUR IGNITION, must be $$$ well spent. I ask, "When was the last time your old Pony ran 7,000 RPM at the track?" The Ford 200/250 has 7 main bearings and can do that with much modification, but they own occasionally-driven classic cars. I feel I am fighting a battle with advertising, and thought you engineer types could be of assistance because I am not an engineer. If I am wrong, tell me. At 75 years I am still learning and building.

 

[Tom.G]

maximum voltage matters little to me, but the guys asking questions on the M6A site,

Well, the higher the voltage will jump a larger gap. If they never re-gap their plugs, replace the distributor cap and rotor, or run with broken/failing resistance plug wires, then yeah, they need as much voltage as they care to pay for. Somehow that does not seem to fit the mind-set of people that bother to ask the question.

Cheers,
Tom

 

[Charlie Cheap]

Tom, we agree. I thought anyone on a site for classic cars would be the type to keep things tuned. I also assumed they would understand the purpose for which they built the thing. Such as car shows, occasionally driving on a Sunday afternoon, or attending a local weekend cruise. You would be surprised at how little today's car-guy knows about the internal combustion engine. For their purpose I see no gain in spending money on something they will never notice. I am also a licensed gunsmith and worked for a city police department for over a decade. Cops are lousy at keeping their firearm in good working order, and it took me weeks of constant badgering to get the chief to force officers to do as I suggested. The day after returning an officers Ruger P-85 9mm to him, he had to use that gun to kill a man, to keep that man from killing his partner. THAT more than anything, got officers to thinking how even in a small 10,000 population town, things can go south very quickly! I have had fun with cars for 60 years, and had my own 100 yard range for 21 years, and I want others to have fun also, while being safe. Guns or cars, safety is paramount. Thanks to all who contributed to my question, and offering places to find what I needed. I need to sleep now, my brain is maxed out!