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45 years ago when I owned my last air cooled four cylinder engine we used to mark the spark plugs so you could “index”, align them in the plug hole to fire in their hottest direction, usually away from the electrode ground.You would index them to fire across the cylinder head. I assume today with the new electrode configurations there is no need to index any more.

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I have been involved with VW aircooled engines (and the hotrodding end of it) off and on for 45 or so years now (a '66 Beetle was my first car in 1974 and within 3 months of purchase we'd put a Holley 2 barrel, 009 and Treuhaft extractor and glasspack on it) and this question/argument/debate has been a topic since before I got involved. For street level performance no one has ever proved it was advantageous.  A high strung racing engine on the ragged edge may be another story, but again, I don't recall anyone ever definitively proving it's worth doing.  I'm not saying it isn't- I just don't remember any data or dyno tests to that end.  Al

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