The cutting of the electrode on the spark plug is to increase the gap, thereby increasing the size of the spark.  We used to do a similar thing with motorcycles when I was still racing.  The larger spark gives a better burn, but make the engine run quite a bit hotter.  You'll probably notice a difference at higher RPMs.

But, besides running hotter, the gap creates a larger amount of resistance, which is hell on an ignition system.  The van will probably run like a rabbit for a little while before the coil (or worse) finally gives out.

IMHO

Brian
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