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Art posted:

Ok, so for dual plugs, you have 2 coils, but only 1 albeit,  8 wire distributor?  That confuses me. but I guess it is just one continuous circle of fire?  And the advantages are smoother firing points?  And what are differences for the plugs? 

I tried to encourage ALB to enlighten me.

The advantages- you can run 1 point higher compression. For example- if the engine will run at 9 1/2:1 single plugged, you can set it up for 10 1/2:1 with dual plugs. The increase in compression gives better power from idle on up. Because of combustion chamber shape (and the spark plug being to 1 side) on bigger bores, with dual plugs you also get a more complete burn throughout the rpm range (2 flame fronts instead of 1), and this translates into more power as well, especially through the upper midrange and top end. Airplane guys who use the VW engine do the dual plug thing for redundancy, and even in their low revving engines find that switching on the 2nd set of plugs typically gives a 50 rpm increase at idle. Type 4 guru Jake R, who was 1 of the first people to work with dual plugs (in type 1's as well as type 4's), claimed something like a 14 or 15% increase in power.

Last edited by ALB
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