Re: Plug indexing

[Jerry Chyo <jerryc@xxxxxxxxxxxx>]

At 05:46 AM 11/26/98 -0500, Paul wrote:
>But surely the inlet valve is open waaaay before the plug fires, and with
>good swirl of the inlet charge to cover the ignition area before the spark
>happens, how can the orientation of the plug make any difference?

Paul,

It comes from the fact that the spark isn't blocked by the stem of the
plugs electrode when it goes off.  This is one of those "little things"
that cummulatively add up (like Red line in the tranny and diff can give
you 2-3 additional HP.)  There's even a kit made by Jacob's Electronic's
that comes with a bunch of different sized "washers" (they call them shims)
that's supposed to make indexing easier.  This is also an old motorcyclist
tip.  Lot's of Harley Sportster guys are into this.

I think it also comes from the fact that hotrodders (and ironhead Sportster
guys) may have been running a domed piston.  The dome gets in the way of
the spark reaching the other side.  That's why you would see lot's of
motorcycles running double plug's.  I guess every little bit helps.

FWIW

Jerry Chyo
'88 M5
'72 tii

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