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Old 02-11-2018, 09:08 PM   #31
40 Deluxe
Senior Member
Join Date: May 2010
Location: now Kuna, Idaho
Posts: 2,660
Default Re: Replacement Ignition Coil

Originally Posted by Purdy Swoft View Post
If this was really the case, no matter what coil or distributor that was used would increase the spark . This is really no so !!! I use a gap of .035 - thats thirty five thousants at the spark plugs . Running at idle speed is not an extra strain on the coil . Idle speed doesn't require extra voltage to jump the .035 gap at the spark plugs. If my Flame thrower coil doesn't increase the spark . Why would the idle rpm increase to the point that I had to readjust the idle speed . I have had similiar results with other performance coils like the 30.000 volt bee hive coils . These coils give performance that a person that has actually used one can't deny .
The increase in idle speed was from opening the plug gap to .035". The increased gap allows for more fuel molecules to be available to be ignited by the spark, so idle speed increases (and emissions go down). In the '70's came stricter emissions laws. One way manufacturers met the standards was with leaner mixtures which required larger plug gaps to cut down on misfire. This required higher voltage coils and in turn better plug wires (most manufacturers went to 8mm wires). EPA also required cars to run longer without a tuneup so electronic ignition systems came into use. Ford went to about .050" gaps , most GM went to .045" gaps, and some Oldsmobiles used .080" for awhile.
Try setting two plugs in your A at .025" and two at .035" and hook it to a scope. Record the firing voltages. Then set the two plugs back to .035". You will see an increase in voltage on those two plugs. Next put on a stock A coil and see if the voltage changes from your 'hot' coil.
When the points open and voltage is induced in the secondary circuit, it only rises enough to jump the plug gap, no matter the coil's potential. With your A on the scope, pull the coil wire out of the distributor cap and watch the voltage rise on the scope as you hold the wire further away. In this case the 'hot' coil will produce a longer spark than the stock coil, because it has more voltage potential in reserve. In normal use, this higher potential is never reached.
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