Quote:
Originally Posted by cn90
Quad electrode: I measure the distance between the electrode and the tip of the prong. It is always more than 0.042". In theory, the quad sounds great, in reality, spark can only jump to one prong. IMHO, 0.042" is too much of a gap...........
.......Then I started doing research for my E39, put NGK Iridium (gap 0.028") a few years ago, engine smooth like silk, no hiccups........
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The larger gap is not an issue.
As I mentioned in my inital post, 2 & 4 prong plugs spark across the insulator surface, there's lower resistance because of surface ion alignment prior to spark.
At any given voltage a spark can jump around TWICE as far across a surface then an air gap.
FWIW, I pulled the OE 4 prong plugs at 105k miles and they looked good, 4 spark paths visible on insulator surface of all plugs.