D
Deleted member 12676
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I got the itch to do my own testing after watching a video of someone testing increased spark with 500pf of capacitance in parallel with a spark plug; https://www.youtube.com/watch?v=tdaN4z8LuQg
Here are my results with three 680pf capacitors in series (each rated 6300 volts) in parallel with a non-resistive spark plug gapped at .025” (.65mm).
Tests were done with spark plug in open air at sea level using my CDI tester.
with KX250F ignition coil (#F6T563) (.3 ohm primary, 13.8K secondary coil resistance)
It didn't increase the spark power but it stabilized spark timing which is important.
Normally there are many stray spark occurrences that are as much as 10 degrees retarded. Those events would cause a reduction in engine power since timing is critical. With the capacitance the sparks all happened at the same timing without any straying. You could see that at the spark also. Without the capacitance the sparks moved around, but with it they stayed at the same place.
KX65 ignition coil (.4 ohm primary, 5.5K secondary coil resistance)
It increased spark power so that the spark changed from thin purple to thick white.
But it allowed the normal stray spark occurrences.
Kawasaki KDX220 (#1G 3960) ignition coil (.2 ohm primary, 11.1K secondary resistance)
Pretty much the same results as the KX65 coil.
None of these coils in combination with parallel plug capacitance worked with my Suzuki AX100 which has 150psi cranking compression. I couldn't get the engine started. All I can assume is that the capacitors lower spark plug voltage so that no spark can occur inside the combustion chamber. (cylinder pressure requires around 3 times as much voltage for a spark to occur*) I even tried it with four capacitors to lower the capacitance to 175pf but without success.
* a flat surface spark gap needs 3Kv for a spark to occur at sea level in open air whereas at 145psi 9Kv is needed.
Here are my results with three 680pf capacitors in series (each rated 6300 volts) in parallel with a non-resistive spark plug gapped at .025” (.65mm).
Tests were done with spark plug in open air at sea level using my CDI tester.
with KX250F ignition coil (#F6T563) (.3 ohm primary, 13.8K secondary coil resistance)
It didn't increase the spark power but it stabilized spark timing which is important.
Normally there are many stray spark occurrences that are as much as 10 degrees retarded. Those events would cause a reduction in engine power since timing is critical. With the capacitance the sparks all happened at the same timing without any straying. You could see that at the spark also. Without the capacitance the sparks moved around, but with it they stayed at the same place.
KX65 ignition coil (.4 ohm primary, 5.5K secondary coil resistance)
It increased spark power so that the spark changed from thin purple to thick white.
But it allowed the normal stray spark occurrences.
Kawasaki KDX220 (#1G 3960) ignition coil (.2 ohm primary, 11.1K secondary resistance)
Pretty much the same results as the KX65 coil.
None of these coils in combination with parallel plug capacitance worked with my Suzuki AX100 which has 150psi cranking compression. I couldn't get the engine started. All I can assume is that the capacitors lower spark plug voltage so that no spark can occur inside the combustion chamber. (cylinder pressure requires around 3 times as much voltage for a spark to occur*) I even tried it with four capacitors to lower the capacitance to 175pf but without success.
* a flat surface spark gap needs 3Kv for a spark to occur at sea level in open air whereas at 145psi 9Kv is needed.
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