Home » Public Forums » GMCnet » [GMCnet] Tid Bit. Will a high voltage output coil make my engine run better.
| [GMCnet] Tid Bit. Will a high voltage output coil make my engine run better. [message #340713] |
Thu, 07 February 2019 13:48  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
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Talking in general term. Not specific voltages. A standard ignition coil can puts out 12,000 volts. An after market high out put coil may state that it has the potential to put out 30,000 volts. Maybe they both cost the same. Well. Is the 30,000 volt coil a better deal? At idle. The spark will jump the spark plug gap at a point that the voltage can over take the resistance that exist at the gap. This will happen at a few 1,000 volts. As the throttle open further. And more air/fuel enters the combustion chamber. Then the piston comes up to compress that mixture. Our GMCs have a compression ratio of around 8 to 1. This means that the air volume that is pushed in by the outside atmospheric pressure. Is 8 times greater then the combustion chambers volume in the engine head. When the piston is at the top of the compression stroke. The density of the air/fuel charge is at the maximum. Thus the resistance for the electrons to travel across at the spark plug gap increases. Next the coil has to produce a higher voltage. This maybe in the 6 to 7,000 volt range. The 30,000 volt coil's extra capacity will not ever be needed, and can't ever be of any value to you. I use a pure stock GM coil on my race engine. At up to 8,000 RPMs. With a compression ratio of up to 13 to 1. The HEI system coil operates at a higher voltage then the points controlled units. This is due to a wider spark plug gap. Bob Dunahugh
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| Re: [GMCnet] Tid Bit. Will a high voltage output coil make my engine run better. [message #340718 is a reply to message #340713] |
Thu, 07 February 2019 14:57  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
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BobDunahugh wrote on Thu, 07 February 2019 14:48 Talking in general term. Not specific voltages.
A standard ignition coil can puts out 12,000 volts.
An after market high out put coil may state that it has the potential to put out 30,000 volts.
Maybe they both cost the same.
Well. Is the 30,000 volt coil a better deal? At idle. The spark will jump the spark plug gap at a point that the voltage can over take the resistance that exist at the gap. This will happen at a few 1,000 volts. As the throttle open further. And more air/fuel enters the combustion chamber. Then the piston comes up to compress that mixture.
Our GMCs have a compression ratio of around 8 to 1. This means that the air volume that is pushed in by the outside atmospheric pressure. Is 8 times greater then the combustion chambers volume in the engine head. When the piston is at the top of the compression stroke. The density of the air/fuel charge is at the maximum. Thus the resistance for the electrons to travel across at the spark plug gap increases.
Next the coil has to produce a higher voltage. This maybe in the 6 to 7,000 volt range. The 30,000 volt coil's extra capacity will not ever be needed, and can't ever be of any value to you.
I use a pure stock GM coil on my race engine. At up to 8,000 RPMs. With a compression ratio of up to 13 to 1. The HEI system coil operates at a higher voltage then the points controlled units. This is due to a wider spark plug gap.
Bob Dunahugh
OK Bob,
Most of this is accurate.
Your reference to firing voltages is correct.
Your summary of the "High Output" coil is correct.
The singular advantage (and the reason for HEI), is that if you have an ignition system that is weak it can leak (bleed off) the ignition energy before it can be used. This is a common cause of misfire. Misfires raise havoc with the HC emissions. It is rare that the compression pressure can get too high for even a weak system to fire, think of your Onan.
Any typical ignition, be it Kettering (Points) or other "conventional" (HEI is conventional with electronic points and a high ratio coil), should be capable to the task. Virtually all the ignition systems in use today are essentially conventional. A great deal of effort has been expended to minimize the leakage and deal with the coil charge time.
The coil works because it gets charged with a power supply that makes it build up a magnetic field. That field is the energy storage. It gets built and maintained until needed by the primary current (what flows though the "points" or other. They all do this. This is where the secondary leakage gets to matter. HEI Immediately went to serious plug wires to fight this. (If you went to buy one in the early years, one wire was the same cost as a whole set of standard wires.) Coil On Plug minimize this by minimizing the secondary harness (wires).
HEI and COP use electronics to control the coil charge but but points have no capability to do this. All they could do was have enough dwell (point closed time) to hopefully charge the coil enough to make it work at high cylinder pressures and high speed. (This is why an Onan works. Those words are not in its vocabulary.)
Here is an easy but not cheap place that the technology is missing the boat. Charging a coil is not the best idea. (L di/dt and all that.) They are not all that good a energy storage. Capacitors are good a energy storage. But to use one directly to fire spark plugs is not simple. (I know, we tried.) A great solution is to use a capacitor as the storage and then use the ignition coil as a pulse transformer. There is one drawback (what makes it expensive in OE terms), to charge that capacitor to the energy needed will take either one HUGE capacitor or very high voltage. With modern electronics, that later is easy to do. So, now you charge things fast at ~300VDC, and then (before it can leak out of the magnetic field) dump that energy into the same coil and it has no place to go but out the plug electrode. This makes for much more substantial spark energy with a very high rate of rise, but as Bob said, more than it takes to start the fire is a waste. That is true until things don't go well. That is where this system shines. If a spark plug is not wanting to fire (for what ever reason), when this jolt hits it, it has little choice.
Well, that is all for right now. I have to go back out to the barn/shop and try to clear away for the next project.
Matt - the refugee from dyno-land
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Tid Bit. Will a high voltage output coil make my engine run better. [message #340733 is a reply to message #340713] |
Thu, 07 February 2019 20:33 |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
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The point of my e-mail can transfer over to many things. I wanted to show in simple terms. That just because some produce is touted as being a great upgrade. Make sure that it really is. How, and why. Bob Dunahugh
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From: Bob Dunahugh
Sent: Thursday, February 7, 2019 1:48 PM
To: gmclist@list.gmcnet.org
Subject: Tid Bit. Will a high voltage output coil make my engine run better.
Talking in general term. Not specific voltages. A standard ignition coil can puts out 12,000 volts. An after market high out put coil may state that it has the potential to put out 30,000 volts. Maybe they both cost the same. Well. Is the 30,000 volt coil a better deal? At idle. The spark will jump the spark plug gap at a point that the voltage can over take the resistance that exist at the gap. This will happen at a few 1,000 volts. As the throttle open further. And more air/fuel enters the combustion chamber. Then the piston comes up to compress that mixture. Our GMCs have a compression ratio of around 8 to 1. This means that the air volume that is pushed in by the outside atmospheric pressure. Is 8 times greater then the combustion chambers volume in the engine head. When the piston is at the top of the compression stroke. The density of the air/fuel charge is at the maximum. Thus the resistance for the electrons to travel across at the spark plug gap increases. Next the coil has to produce a higher voltage. This maybe in the 6 to 7,000 volt range. The 30,000 volt coil's extra capacity will not ever be needed, and can't ever be of any value to you. I use a pure stock GM coil on my race engine. At up to 8,000 RPMs. With a compression ratio of up to 13 to 1. The HEI system coil operates at a higher voltage then the points controlled units. This is due to a wider spark plug gap. Bob Dunahugh
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| Re: [GMCnet] Tid Bit. Will a high voltage output coil make my engine run better. [message #340742 is a reply to message #340713] |
Fri, 08 February 2019 08:16 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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There is a point (no pun intended)to consider here, and that's the quality of the components, particularly the coil and other high voltage parts. Consider the 30KV coil from the Heathen Chinee. It makes 30KV, which erodes the cheap varnish they put an insufficient amount of on the HV wires. So, eventually, the insulation breaks down, the coil shorts either partially or totally internally and no more or much weaker spark. But that 30KV sure sounded nice.
Now, if you want to light the fire more reliably, and don't mind wiping out everyone's radio fro a mile around, find some copper conductor spark plug wires. Reset the timing and they will light every time.
Note that the Delco coils were built to a fairly stiff spec, consequently they work. The heathen chinee were built to whatever spec they thought they could get away with. The CDI systems work well, but they're more c0mplex.
It's always worth taking the engine hatch cover off when it's dark out and turning all the lights off and crank the engine. Any place you see a blue haze, replace the wire or component - it's leaking.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Tid Bit. Will a high voltage output coil make my engine run better. [message #340744 is a reply to message #340713] |
Fri, 08 February 2019 08:40 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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The problem with turning your vehicle into what I call a "Jegs mobile" shopping catalogs for "bigger and better" everything is that you upset the engineered balance in the system. Like Bob said, only a portion of the coil's potential voltage rise gets used in a properly running system. When the primary power opens, the mag field collapses and voltage rises in the coil windings (plural) until it finds ground, hopefully at the plug gap. I say plural because the colapsing mag field cuts through the windings of both the coil primarily and secondary and voltage rises in both until it dumps to ground. Hopefully not within the coil itself. The event (aside from some smaller resonance activity) is then over. The harder it is for the gap to jump (many factors including parts condition and cyl pressure and mixture) the more the voltage rise of back EMF to the points/cond or electronic switch device in the module. This is factored into system design to withstand X number of missfire events with full coil rise. You will recall the GM lowered gap spec from the initial .080 which was found to be marginal have problems in the real world once the suggested service interval was approched and stretched by owners. So the hypo aftermarket coil may help fire the plug in "extreme conditions" as advertised but at the expense of reliability of other system components which will then leave you roadside dead. They often recommend matched hypo modules to go with the coils, but personally I prefer a genuine GM module, especially one that has proven itself over time. Personally I have been driving HEI since 1976 and never had a failure on the integral coil type. The only fail I had was on a just "new to me" Tahoe with the external coil. The HT lead from the coil to the cap vaporized itself at one end probably due to corrosion. In such a case the hypo aftermarket coil would have probably caused other system damage. In this case a new wire set, cap and rotor was a cheap fix.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Tid Bit. Will a high voltage output coil make my engine run better. [message #340748 is a reply to message #340713] |
Fri, 08 February 2019 10:06 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Let's also point out, the box stock GMC HEI ignition is a rock reliable piece. There are a zillion of them still on the roads with an extremely low failure rate. The stuff I find fails is/are pretty much aftermarket. Particularly aftermarket rotors with substandard center posts. They wind up with arcs and sparks and little or no function. The Delco rotor costs a bit more but will run much longer without problems.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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