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  #1  
Old 11-09-2005, 04:18 PM
SteveBuchanan SteveBuchanan is offline
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Hi,

I have some concern about the color of the spark from my ignition system. I have MSD 6A, Blaster 3 coil, and Autolite 3924 spark plugs with a gap of 55. I have read that the spark should be blue, or even white. The color of my spark is more towards the orange side and I have read that this indicates weak voltage. I am conducting this test from the coil output and thus bypassing the distributor as a possible source of voltage loss.

Is it valid to evaluate spark color in this manner? Is there a better way to test voltage output from the coil?

Thanks!
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  #2  
Old 11-09-2005, 06:05 PM
bill jones bill jones is offline
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-When you check the spark at the coil wire---if you have an 8 cylinder engine---then you have 8 times as many sparks happening at the gap for whatever rpm you are testing at.
-As a spark jumps it ionizes the air---burns up those airbborn resistances to the spark---so the next spark can get thru there a lot easier----so having 8 times as many sparks means you have nearly no resistance left against the spark so the spark flows VERY easily.
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-When you break up the spark 8 times using the distributor cap and rotor and 8 plug wires---then the red goes away and you see the blue or yellow because now the resistance is still there to the spark and a higher energy (more voltage) is needed to get across that gap each time.
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-I read somewhere that it takes 20,000 volts to jump a 1" gap at sea level so if you are testing in open air you need to increase the gap well beyond the .055" of the sparkplug.
-When I test on my distributor/ignition machine I use a gap plate that is moveable to increase the gap during any test.
-I usually always start out at a short gap---maybe .100" and then when I really want to make sure the spark is going to go wheres it's supposed to I open the gap to about 13/16" as the absolute max but usually feel like about .650" is plenty good.
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-I sort of feel like you have to compensate in open air for cylinder pressure so I simply take compression ratio times the plug gap you intend to run for my baseline testing of that ignition system.
-Example is if you have a normally aspirated engine with 14:1 compression and a .055" gap I'd multiply those numbers and use a gap of .770" in open air at each of the 8 plug wires.
-I use fairly small pointed ends on my gap plate so the spark knows exactly where it wants to go.
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-When doing any serious testing I always like to do it in total darkness so I can locate the various coronas and get an idea of how prominent they are and I always have a cap that I can view inside to see the activity of the rotor path.
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-I seriously doubt that MSD cares much for my method of testing but I have found that when all 8 sparks will jump the big gap and not wander off to something else that is metal and grounded---and go past the rpm I am wanting---that I usually have a pretty decent system.
-One thing about this is it is pretty damn scary and you don't want to even think about getting your finger in there or even breathing your nice moist breath close to that spark activity.
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-I don't believe using just the coil wire jumping to ground is a valid example of what the ignition power is all about.
-Many ignitions I test will NOT jump the gap I'm looking for it to---so I have to work on the details and the components to get there.
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  #3  
Old 11-09-2005, 06:40 PM
donj donj is offline
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Bill is giving you great advice. I agree with everything he's telling you and that is rare, with one clarification you probably don't really care about. (The TOTAL number of sparks will be the same at the coil or the plugs, BUT - at the plugs they will be distributed to eight places and at the coil they will all be at the same place.) You can learn something from this guy!
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Old 11-10-2005, 09:04 AM
SteveBuchanan SteveBuchanan is offline
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Yes, it makes good sense what Bill is saying. I was doing some testing last night in the dark and could see the behavior he described. When holding the coil output to the engine block, there was an almost constant, hollow, 1/16 diameter arc. And that was only cranking the engine. I then ran the engine holding one plug near the block and saw the reduced activity. The spark was considerably reduced in size.

My real objective here is to determine if my ignition system is operating at full capacity. Someone told me that the voltage at the spark plug can be measured with a relatively inexpensive tool. If the voltage output is far away from the rated output for the coil, this would point to potential problems with the cap, rotor, or wires. So, is a visual test of spark at the plug sufficient or is a measuring tool better?
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  #5  
Old 11-10-2005, 09:29 AM
bill jones bill jones is offline
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-you run into some issues when checking at the end of the sparkplug wire.
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-I would propably say to slip a a paper clip into the plug wire boot touching the metal terminal end of the wire to where you can ground the spark with a WELL INSULATED screw driver that has a positive grounding wire attached to it for the test.
-I would also lay the shank of the screwdriver on grounded metal and wear some sort of well insulated gloves when you are making the spark jump a gap.
-When you get that spark to jumping if it bites you once you'll fully understand why you need to be precautious.
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-Issues are the MSD is a multiple spark and it switchs down in spark count at rpms like until about 1100 there is more than 3 sparks in succession---then at 1100 or so the sparks drop to 3 in succession until about 2200 then it switches down to two sparks until about 3300 when it goes into a single spark for the rest of the rpm range.
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-So I would want to test the spark at something like 3600 rpm and then see what sort of gap you can make with the single spark jumping at the end of the plug wires and then decide what the color of the spark is.
-You will probably be surprised that the spark will jump a pretty wide gap and doing this sort of testing you are likely to eventually get a zz-zz-zz---zzap and end up with a dead box.
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-I would NOT try to see how long of a gap you can get the spark to jump---just do the compression ratio times plug gap and use that for your max gap number---at any rate don't worry about making it jump any more than about 5/8 to 3/4".
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