If you are old enough to have used a Sun scope, then you might remember this little gimmick that used to be sold through Pep Boys, JC Whitney and the like that you put between the coil wire and the distributor cap that was supposed to increase your spark intensity thereby giving you more hp and gas mileage. It was just a spark gap. I bought on when I was 16, didn’t work, as did any of the other cheap little add-ons sold at the time.
Anyway, I got my hand too close to it one time and it knocked the snot out of me. A lot of things that made sense at the time didn’t work for reasons I learned later. Education is expensive, but worth it.
Thanks for all the replies. I now have a good grasp of why it works. I don’t fully understand it but it’s one of those things that should not work but it does. I do remember those little gizmos for the coil but they never worked for me. I bought a couple of old junkers with those things attached. I took them off and threw them away not fully realizing the tremendous power I had in my hand. Live and learn.
I lurk around on this site often, mostly skipping by questions because I don’t have the patience to answer them or I decide the poster wouldn’t understand or try to do what is suggested. Then something like this string comes along, and I understand why I’m here. I now have some slight understanding of the physics of electricity in a points and coil system, which I never really understood all the way. And I thank you all for the discussion, especially “keith”.
A scope is a wonderous thing. There’s truely nothing like a trace across the magic phosphors to see what’s really going on. I’m a humble servant of the traces. Perhaps that’s my electronics background driving me.
Rod, have you looked at the trace beyond the additional gap in the circuit? Does the voltage at the plug show a higher spike? If you have looked there, I’ll accept your word and the saturrated coil theory, even though I’ve been arguing against it.
Speaking of coil wire tricks, I saw a coil wire replaced by a lenght of vacuum hose and the car ran, my theory is that the air inside the tubing became ionized (took either a postive or negative charge) and conducted. It was a pretty good show as the guy took bets if the car would run, the bets went 50/50
I can tell you that I have a robe that when worn on a dry winter’s evening can generate a sufficient charge to jump a 1/16" or greater arc to earth ground when I go to turn on the hall light. It lets me sleep well at night knowing that box is grounded…
Yeah, Keith, I forgot that heat and temperature are two different things. So even with a longer spark duration, where the spark temp is cooler than in the scenario where you have less circuit resistance, there may be more heat applied to the fuel.
I have a military background in electronics and have watched many an ignition system dance across an oscilloscope screen…My post was and is accurate… Until current flows in a circuit, there is no “circuit”… With the coil wire removed slightly, no current can flow in the secondary so the voltage can rise to VERY high levels…With the coil wire in place, there is a path for current to flow, through the insulator of the fouled plug to ground. Under these conditions, the voltage in the secondary circuit never rises high enough to jump the air-gap of the plug…
You talk about series resistance…An air gap has INFINITE resistance! But once an arc forms across the gap, the resistance drops to almost zero as current flows in the arc’s plasma…
By preventing current flow in the secondary circuit, voltage is forced to climb to the highest possible level, high enough to fire a fouled plug…But don’t take my word for it, you can set this up and watch it happen on an oscilloscope screen…
When an air gap is made in the secondary the voltage spikes while the length of time the spark remains on the plug is shortened. If the air gap is too great for the coil to jump the spike will indicate the maximum output of the coil but the voltage line will make a slightly curving slope and then drop nearly vertically back to ZERO and below and then oscillate +/- as the coil disipates. When using a distributor tester the plugs can be viewed as they fire and compared to the scope pattern.
The pattern of a point type ignition in normal parade setting begins with the flat line near zero, when the points open the voltage jumps to 6,000 to 10,000 depending on the plug gap and compression. After the initial spike, voltage drops approx 30% from maximum and “dwells” in a nearly horizontal line as spark remains on the plug. When the spark ends the voltage drops and oscillates 3 to 7 times as the coil fully dischargew, when the points close, the line is horizontal at that time and with a bright vertical line it drops slightly, entering the dwell period of about 60% of the parade period. It’s been many years since scoping a point type ignition but I feel my memory is accurate on this.
Right you are Knox…Thanks for supporting my earlier statement that an extra, created, air gap will cause the VOLTAGE (the vertical scale on a 'scope) to climb towards maximum possible. This higher voltage is felt at the plug too, after an arc forms across BOTH air gaps…
“Excellent post, Keith. You cleared up what had always been a mystery to me: Ohm’s law says that in a series circuit voltage progressively drops across the resistance portions of the circuit, but that at any given moment amperage is the same everywhere.”
But with Missileman’s air gap, there is ZERO current flow…So the VOLTAGE is stopped at the distributor cap where the wire has been lifted…Only when the voltage climbs high enough to from an arc, then current flows across BOTH air=gaps at the same instant…
Without Missileman’s air gap, current is FREE to flow across the wet insulator of the plug as the voltage tries to climb. If enough current is able to flow, bleeding off the voltage, it will not get high enough to jump the air-gap…
Speaking of spark plug tricks.
Back in 1973 we had a guy from Champion spark plugs come and talk to our class at the 2-year auto mechanics school I attended. At the end of his talk and Q&A, he did a little demo for us. He had a lawnmower engine with 4 feet of spark plug wire. At the 2-foot halfway point, the two ends of the spark plug wire were cut and barely tied back together (so they could be pulled apart easily).
He started the engine, then held the spark plug wire in a loop such that much of the wire in the loop was close and parallel.
Then he pulled the wire apart at the 2-foot point. (There was no longer a wire connection from the magneto to the spark plug.) With much of the length of the two halves being close to each other, the engine never skipped a beat. It kept running just as smoothly as it did before.
He then separated the two wire halves so they were no longer close to each other, and the engine began to die. Then he’d bring the two halves closer together and it would run again.
That was my first real life exposure to how important magnetic induction really is.
You guys have brought back alot of memories. I’ve used this method to start flooded cars many times in the past. The blue ark and buzz was always a great show for novice mechanics.I had to laugh at old shcools response about the vacuum line carrying spark. I wouldn’t believe it if it had not happenened to me.
I don’t want to get into a credentials contest with you, but I too have military experience in electronics and then some. I am sorry that I slammed you, I don’t usually do that and for that I apologize. But do go look at your first post with a critical eye and I’m sure you will see several errors.
I do see some “bad gouge” in both of your posts that passes through the military schools. It comes from instructors that can’t understand the lesson guides. I rewrote several lesson guides for the Navy’s advanced electronics school (AVIC-7) because of the crap that was in it. Unfortunately, some of this misinformation made it into the advancement tests.
Spark gaps do not go from infinite to zero ohms, they go from high to lower. Flooded engines do not necessarily had the spark plug gaps bridges with gas, they usually just get wet. Gas does not have zero resistance. The issue isn’t that a spark does or does not form, the issue is whether a spark forms while the fuel air ratio is between LEL and UEL (lower explosive limit and upper explosive limit). In older carbureted cars, the fuel distribution wasn’t as uniform as it is with fuel injection. As the fuel and air swirl around the spark plug tip, you hope for the fuel air ratio to be between these limits when spark occurs.
In a flooded engine, the fuel air ratio is mostly above this limit. A longer duration spark increases the odds that you will catch the fuel air ratio when it is between these limits.
As for your last sentence, two gaps in series still form a voltage divider.
That is a primary trace. It is taken from the primary side so it is about 1/100th of what would be at the top of the coil. It does not represent what is happening at the spark plug gap.
Keith and Caddyman both make good points. I believe Keith is right about missleman’s extra resistance making the rotor-to-distributor electrode gap and the spark plug gap resistance go from high to lower as opposed to going from high to almost zero.
This is born out by the fact that with a Sun scope, for example, a typical firing line voltage value (amount of voltage needed to ionize the gaps) might be 12kV, but when the gaps are ionized and the spark jumps, the voltage is then much lower, say 5kV. But a spark with 5kV certainly indicates one heck of lot more resistance than something close to zero!
Here is a cutaway image of a spark plug. You can see how, if the insulator that surrounds the center electrode was wet, the secondary circuit could could possibly make a complete circuit without the spark jumping the gap, This supports Caddyman’s assertion regarding this issue.
Also, I did some reading up, and it seems that as the firing voltage increases (due to more secondary circuit resistance) the spark duration decreases, and vice versa.
Man you told him right on the carb,could probaly get decent performance performance with a smaller correctly jetted carb then that(look what Nascar runs) ditto on the resistance making a fatter spark
