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Why a HOTTER Spark

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BUDD

10-24-2002 17:49:19




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I am well aware that put a "hotter" coil will increase a little HP. The problem is I have never figured out why. As long as I have a spark and it ignites the fuel, what good is a hotter coil going to do. You can only light the fuel so much (one time)? In my small block chevy I have a 50,000 volt coil and I don't know other it looks good under the hood. "Inquiring Minds Want To Know"

THANKS BUDD

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John T

10-25-2002 12:10:07




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 Re: Why a HOTTER Spark in reply to BUDD, 10-24-2002 17:49:19  
Budd, my August Green Magazine artice titled "In Search of that Hotter Spark" answers much of your question, but I will give a brief answer here. First, regardless if you have a super duty expensive so called HIGH VOLTAGE coil, the coil voltage will only ramp up as high as required to arc jump the plug gap which may be more like 10,000 to 15,000 volts. A so called super or high voltage coil wont fire the plug at any higher voltage then your stock coil. And, unless the efficiency and mutual inductive coupling is way higher in the super over a stock coil, it wont be at much higher amperage either. A high voltage coil has sufficient windings and winding ratios and core material to produce a potential higher voltage at its output, but you would only realize such by a much wider plug gap than normally ran in the tractor. As my article points out, its HEAT which ignites the fuel/air mixture, and thats due primarily to arcing current, not whatever voltage must be achieved to jump the gap. What a high voltage coil can do if coupled with a high energy solid state ignition, is produce a "hotter spark" which consists of higher current and across a wider gap which requires that higher voltage to arc across. Therefore, you get a fatter, hotter, longer more surface area current arc which better ignites the fuel in high compression or exotic fuel situations. In the stock situation, if you widen the plug gap forcing the coils voltage to rise higher to jump the plug gap, the arcing current is reduced to a lower temp yellow as opposed to a higher temp blue spark. Thats why the recommend plug gap is designed for the compression, fuel, and coil voltage etc parameters so as to best ignite the fuel. A higher voltage wider plug spark produces less current in that stock system. Bottom line is, if you stay with a stock coil/points ignition, a so called high voltage coil will fire at the same voltage (so long as plug gap is same) and not help you much. However, if you drastically increase the compression and/or run exoitc fuels, then a high voltage coil coupled with a higher energy solid state igntion, will buy you alot. You can then get a longer (wider gap) fatter hotter sprak of more current and heat Good Luck. Ol John T Nordhoff, Engineer in Indiana.

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Roger Olson

10-25-2002 03:22:00




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 Re: Why a HOTTER Spark in reply to BUDD, 10-24-2002 17:49:19  
Opinion #4:
You start out with a certain amount of energy, based on your type of ignition system, i.e., coil, electronic, etc. A cylinder under compression presents a good insulator at the spark gap. The higher the compression, the better the insulator. The leaner the mixture, the better the insulator. As the coil secondary collapses, a certain voltage will be enough to ionize at the plug gap and begin the spark or current flow. The voltage drop at the plug immediately drops to only a few kilovolts. Now you have a current flow that can last around 2 miliseconds. This is called the burn time. The spark is more of a ZZZZZT than a crack. If you start out with more voltage quickly available to start the spark, you'll ensure there will be enough left for the burn time. As the fuel mixture is swirling and ignited, this "burn time" lights off more of the fuel to make a larger flame front. This doesn't necessarily light the fuel faster, but more completely. The fuel can only burn at a certain rate, based on type of fuel, compression ratio, etc. This is why most gasoline engines have a total ignition advance of around forty degrees.
Bottom Line - the more energy available- the more complete the combustion.
PS - Ive installed around 20 MSD systems. They're much more effective on higher compression, built engines. I have one on my old ford truck. Don't see much difference in performance, except it starts up before you can let off the key. Impressive!
Roger

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John T

10-25-2002 12:26:42




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 Re: Re: Why a HOTTER Spark in reply to Roger Olson, 10-25-2002 03:22:00  
Roger, in your opinion, on my motorhome which has a stock 460 Ford Engine using stock regular unleaded fuel, would an MSD or Jacobs ignition help much with fuel mileage??? MY personal engineering intuition tells me NOT MUCH (I know why they help in high compression, exotic fuel, high rpm applications), but would like to hear from one who has used them. My best help comes from running dual 2 1/2 exhaust with free flow mufflers, double platinum plugs, not runnong over 60 mph (wind drag is a function of velocity squared I think) and superb tuning and timing. Ol John T Nordhoff in Indiana

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Roger Olson

10-27-2002 03:13:47




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 Re: Re: Re: Why a HOTTER Spark in reply to John T, 10-25-2002 12:26:42  
John,
I didn't see your post on "In Search of a Hotter Spark" until now. I see you know your spark.
My experience is mostly in testing with hardware I've built and cars I work on almost daily(hobby gone bad) for the past 15 years. My education is in electronics, although I was a professional mechanic.
Do you remember the old AC Spark Plug Cleaner and Tester? Pretty neat unit to play with. I have one that's a little more sophisticated that I hook to my scopes. This helps me troubleshoot and find leaks in wires, caps, plugs, etc. One interesting thing I've discovered is with Champion Truck Plugs(don't bother). There's a gold colored logo band about half way up the plug, on the outside. If the wire boot end is not super tight, the spark travels down the outside of the plug, using the band as a steppingstone to ground. This shows how bad the environment inside the cylinder is. The spark would rather take that long journey on the outside. Loose boots are common problems for bad spark. On one, I found some GM wires on backwards(the "dist" end really needs to go to the distributor end} and misfiring under load at the plugs. The boots had a larger ID and the spark traveled right down the plug to ground.
In all the testing I've done, I find the condition of the plug electrode to have the most influence on the ability to spark. As you know, a spark or electrons will leave a sharp point much easier than a rounded point. I,ve seen the firing voltage drop by half, just by filing the electrode flat(sharp edge on the circumference) and maintaining the same gap. The platinum plugs naturally do better with the smaller electrodes(more pointed)and the fact that it is a platinum electrode. Changing the gap by 20% results in only a few kilovolts rise on a clean plug. On an old style plug, with a rounded electrode, the rise is much greater for changes in gap.
Todays ignition systems are are kinda like a good stereo, all the loads and impedences are matched. The efficiencies are much greater. Dwell time is longer and dutycycles are down. Hard to improve on this.
The MSD Ignition Systems fire full voltage(whatever is necessary at the time), multiple sparks at the lower rpms, and drops to single sparks at the higher rpms. At lower rpms, in a loaded condition, multiple sparks will ensure good combustion. I think this is why I see better performance on built engines, especially off the line. The very worst conditions for good sparks are happening with the higher compression ratios and packed cylinders and low rpms. Wow! There's some ramblin'
I agree with you on your motorhome. It will take a while to pay for an MSD System with an almost undetectable change in performance. Sounds like you keep it in pretty good tune.
Good Luck,
Roger

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Clooney

10-24-2002 18:14:45




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 Re: Why a HOTTER Spark in reply to BUDD, 10-24-2002 17:49:19  
Budd, a hotter coil won't make more horse power without other changes such as different plug gap, higher compression, or other changes that can use or need a hotter spark. The exception is a MSD system that gives multiple sparks.
~Now if you are getting misfires due to low coil KV then a hotter spark will help.
~Basically electricity is lazy & won't build any higher than needed to jump the plug gap. So a 50,000 volt coil will only build to 15,000 volts if that is all it takes to jump the plug gap. The coil response time can have an effect on the spark & if an electronic ignition is used in conjunction with a higher voltage [output] coil the spark can be so intense it will even fire a fouled plug as it has so much reserve it can lose some KV to bleed off & still jump the gap. A conventional point/condenser system has a rather slow coil build & collapse time & can allow the spark to bleed off down the center electrode before it builds high enough to jump the plug gap. An electronic system uses a transistor to switch the coil circuit & allows a higher primary current than a point system could handle. A higher primary current means a higher secondary output in most cases. The down side is heat [more output &higher KV means more heat to dissipate]

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ChuckW

10-24-2002 18:14:20




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 Re: Why a HOTTER Spark in reply to BUDD, 10-24-2002 17:49:19  
I think of it in the sense that the fuel/air mixture is trying to drown/short out the igniter, therefore a stronger ignition will prevent this and cause rapid burn.



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lonnie

10-24-2002 18:11:11




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 Re: Why a HOTTER Spark in reply to BUDD, 10-24-2002 17:49:19  
The reason a hotter spark is needed is that when the fuel air mixture is under compression,with out a hot enough spark it may "blow out" the spark.Just look at top fuel dragsters, They use two hot magnetos just to make sure they get a complete burn of fuel in the combustion chamber & we all know that top fuel is a pretty high compression engine. Low tension mags work on some of the hit&miss engines because they have very low compression ratio somewhere around 5:1 or less. I believe the John Deere H only has 4.75:1 cr. If I am wrong abotu any of this correct me please.

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Keith G.

10-25-2002 10:21:51




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 Re: Re: Why a HOTTER Spark in reply to lonnie, 10-24-2002 18:11:11  
Actually, Top fuel has low static compression, it's when the rpms come up that the blower forces more air & fuel into the cylinders which causes higher cylinder pressure not higher compression. I still don't understand fully all this myself but that's the way it works. Keith



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Keith G.

10-25-2002 10:23:25




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 Re: Re: Re: Why a HOTTER Spark in reply to Keith G., 10-25-2002 10:21:51  
It's the higher pressure not compression the blows out the spark.



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