Slant Six Forum :: Spark Plug Gap Question

Quote:

Get a hotter spark from a more powerful ignition, but leave the gap alone.

I'm sure you know this already, it's just that what you wrote was ambiguous on the point: Remember, for any given spark plug gap, under any given conditions, it takes a certain voltage level to jump the gap, and it doesn't matter whether you have breaker points or a $1000 computerised distributorless ignition system, there's no such a thing as forcing more than that voltage across the gap. So, no, you don't really get a "hotter" (higher voltage) spark from a more powerful ignition without increasing the plug gap. You might get a higher-current spark (more amps) but under most conditions that doesn't do much but wear out spark plugs faster!

Assuming that the resistance across a certain gap is fixed and the voltage required to ionize the gases in that gap so that current can flow is fixed

Quote:

Assuming that the resistance across a certain gap is fixed and the voltage required to ionize the gases in that gap so that current can flow is fixed

Both bad assumptions inside a combustion chamber of constantly changing volume, full of a turbulent inconsistent fuel/air mix which begins to ignite during this process.

When someone asks what to gap there plugs at, they would not be asking if they knew ignitions inside and out. They just want to keep their car running well and do it themselves.

You and I both know (and I gather agree) that the secondary side of the ignition needs to be kept in top (or at least very good) shape to run larger gaps.

Many people will not, however, want to buy more expensive plug wires or get the best cap and rotor.

And really, you will get a hotter spark with a better ignition no matter what the gap.

whatever is done should be done right

Author:	Ron Parker [ Tue Sep 26, 2006 6:56 pm ]
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Thanks Dan Ron Parker It Aint Over Until I Win

Author:	dakight [ Tue Sep 26, 2006 7:30 pm ]
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Quote: Quote: Get a hotter spark from a more powerful ignition, but leave the gap alone. I'm sure you know this already, it's just that what you wrote was ambiguous on the point: Remember, for any given spark plug gap, under any given conditions, it takes a certain voltage level to jump the gap, and it doesn't matter whether you have breaker points or a $1000 computerised distributorless ignition system, there's no such a thing as forcing more than that voltage across the gap. So, no, you don't really get a "hotter" (higher voltage) spark from a more powerful ignition without increasing the plug gap. You might get a higher-current spark (more amps) but under most conditions that doesn't do much but wear out spark plugs faster! Not to nit pick your point Dan, but don't forget Ohm's law. Assuming that the resistance across a certain gap is fixed and the voltage required to ionize the gases in that gap so that current can flow is fixed then the current that flows will also be constant. I (current in amps) = E (voltage in volts) / R (resistance in ohms)

Author:	Joshie225 [ Tue Sep 26, 2006 8:19 pm ]
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David, Ignition systems are kinda funny and simply applying Ohm's Law will lead you astray. One fundamental problem is that the coil will only store so much energy in it's magnetic field before the coil current is switched off and the magnetic field collapses. When the magnetic field collapses the secondary voltage rises until the spark plug and rotor to distributor cap gaps inonize at which point the voltage drops and the current increases. A higher voltage coil cannot change the voltage at which those gaps ionize. Also, a higher voltage coil for a given input power is necessarily a lower current coil. For our not very demanding slant 6s the current is more important as the spark lasts longer.

Author:	slantvaliant [ Tue Sep 26, 2006 9:05 pm ]
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Quote: Assuming that the resistance across a certain gap is fixed and the voltage required to ionize the gases in that gap so that current can flow is fixed Both bad assumptions inside a combustion chamber of constantly changing volume, full of a turbulent inconsistent fuel/air mix which begins to ignite during this process.

Author:	dakight [ Wed Sep 27, 2006 7:55 am ]
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Quote: Quote: Assuming that the resistance across a certain gap is fixed and the voltage required to ionize the gases in that gap so that current can flow is fixed Both bad assumptions inside a combustion chamber of constantly changing volume, full of a turbulent inconsistent fuel/air mix which begins to ignite during this process. I understand that conditions change inside the combustion chamber and that the electrical characteristics are highly variable but I'm talking about the difference between ignition systems. Under the same conditions of temperature, pressure, and gas mixes, the resistance across the gap will be the same whether you have a simple points system or a high dollar, high output system. Obviously the high output system will perform better under adverse conditions because it can generate higher voltage to overcome the higher resistance but that's not the point. The point is that for a given resistance and voltage, which is the ionization voltage across the gap, the current will also be fixed by ohms law. Now Josh says it's not that simple and he may be right, it's entirely possible, perhaps even likely, that the resistance will change as the combustion process develops within the chamber, but the voltage, current, and resistance are still governed by ohms law. If one parameter changes, the others will change to maintain the relationship as stated by ohm's law. Also, I realize that I've completely ignored spark duration. The voltage and current will follow a decay curve from the peak voltage required to ionize the gap until the current has compltely discharged the coil. That curve will no doubt be different for different ignition systems which is really the whole point for using them in the first place, but the initial spark voltage and current will be identical under the same conditions regardless of the ignition system driving it, provided that they both can generate enough energy to ionize the gap and start the process. What happens after that is another matter entirely.

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Author:	slantvaliant [ Wed Sep 27, 2006 9:09 am ]
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Yes, Ohm's Law applies. Throughout the process.

Author:	AnotherSix [ Wed Sep 27, 2006 11:58 am ]
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I thought my points were clear. Dan, you seem to want to just take small parts out of context and take issue with them. I am not sensitive. My point (here it is): When someone asks what to gap there plugs at, they would not be asking if they knew ignitions inside and out. They just want to keep their car running well and do it themselves. You and I both know (and I gather agree) that the secondary side of the ignition needs to be kept in top (or at least very good) shape to run larger gaps. Parts don't stay new forever. I assume you keep everything on your vehicles in top shape and work on them often, I do as well. Most people don't. Your info about a better rotor is the kind of detail I pay attention to, and is something I can use. Many people will not, however, want to buy more expensive plug wires or get the best cap and rotor. Yes it can all be done, I just do not agree it is the best advice for everyone. How long is the service life of your plugs with the wider gap? If it is shorter than normal I would include this info along with the advice to run a wider gap. Running a .045" gap does not leave much room for wear or increased resistance from deposits. And really, you will get a hotter spark with a better ignition no matter what the gap. This is not a "maybe". Yes it starts to arc at the same voltage regardless of the ignition, but the stronger ignition will dump more energy across the gap (whatever it may be) and give a hotter spark. Voltage to strike the arc does not determine how hot it will be, the amount of energy being dumped does. Even the stock coil will produce much more usable energy when driven by something better than points. When the voltage drops it will hold the arc longer with a tighter gap as well. When the magnetic field in the coil falls, all the energy has to go somewhere. By getting as much as possible across the gap less of it ends up as waste, mostly in the form of heat. I am sure you have seen the difference between a weak yellow spark and a bright blue spark? It's not just the voltage! Anyway, I appreciate the sharing of thoughts, but lets not push facts aside just to be right.

Author:	Slanted Opinion [ Wed Sep 27, 2006 5:17 pm ]
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Once the spark "makes the jump" the ionization of the mixture in the area of the spark should lower the resistance, causing the current to increase and the spark to be maintained even as the voltage rapidly falls away. Makes me think of neon lamps, which we used to fire off at (I think) 70 volts, but would then stay lit at a much lower voltage. Of course, the gasses in a neon lamp aren't under so much turbulence! My 2 cents. -Mac

Author:	SlantSixDan [ Wed Sep 27, 2006 8:48 pm ]
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Quote: When someone asks what to gap there plugs at, they would not be asking if they knew ignitions inside and out. They just want to keep their car running well and do it themselves. "What spark plug gap should I use?" can have different meanings, depending on who's asking it and in what context. It can mean "I don't have access to a FSM and need to replace my spark plugs today, what's the factory spec?". It can mean "I'm running the following nonstandard ignition system and want to know what'll optimise my driveability and mileage". It can mean "I'm trying to shave a tenth off my E.T.". It can mean "I'm getting a weird engine stutter/falter just above 5,000 RPM and think the spark plugs are involved". Let's neither of us presume to put words in the mouths of all however-many-thousand users this board has. Quote: You and I both know (and I gather agree) that the secondary side of the ignition needs to be kept in top (or at least very good) shape to run larger gaps. Mmkay, let me try again: There are larger gaps and then there are much larger gaps. There is no significant increase in the rate or degree of ignition component deterioration from running a gap of 0.040" rather than 0.035" if you have electronic ignition of any kind. If you have points, the points won't last quite as long, but they'll still give you over a year's service, by which point the rubbing block will have worn such that they should be replaced anyhow. You and I can argue from now until the cows come home over 0.045" gaps, but what's the point? Yeah, if you run 0.045", you want to use the longer-tip rotor, and your distributor cap might last 2 years instead of 3, meanwhile you're getting better driveability and mileage. You spend your money on gas, I'll spend it on an extra cap and rotor, and after the three years is up we'll go split the bill for a couple pizzas and pitchers of beer, 'k? Quote: Many people will not, however, want to buy more expensive plug wires or get the best cap and rotor. Disagree. This board gets a steady stream of "What's the best (part) I can buy for my (year, make, model)?" type questions, but very few "What's the cheapest" types. Quote: And really, you will get a hotter spark with a better ignition no matter what the gap. H'mmm. Are you, like, tryin' to find stuff to argue about with me? Not interested, thanks. I'm tired. Been flyin' all day.

Author:	AnotherSix [ Thu Sep 28, 2006 12:23 pm ]
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Well, that sounds like a good kind of tired! No, there is nothing to argue about. Like I said before, it's YOUR car, and I mean about everybody. Do what will hopefully make it perform the way you want and make yourself happy with it. My opinions are tempered by the experiance of giving what I know is good advice but having only part of it followed. So they end up without the combination that works. Then the person comes back and wants to know why it didn't work for them like they've seen it work on my car. Not only did they waste their time, but mine also. If you look back I think you will see that I was arguing about what could or could not be done, just trying to be clear that whatever is done should be done right, thats all. We must agree on this? Not that we have too.

Author:	SlantSixDan [ Thu Sep 28, 2006 12:53 pm ]
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Quote: whatever is done should be done right Sold! Now let's go get that pizza and beer.

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