[Harp-L] Gapping & Embossing and the "three angle valve job"

["Aongus Mac Cana" <amaccana@xxxxxxxxxx>]

Car buffls and hot rodders will be aware that hogging out the inlet ports is
the conventional starting point for extracting more power from a stock car
engine.
However two engineers published a paper in the Institution of Mechanical
Engineers about fifty years ago where they established that merely rounding
off the corners on the inlet valves and their seats - the so-called "three
angle valvejob" substantially increased gas flow without any other
enlargement of the ports - particularly at low lift.
l think it was Rick Epping who  remarked some months ago that Hohner found a
noticable effect on performance  of harmonica reeds caused by slight
chamfering of the reeds. Of course the embossing process would also cause
chamfering of the reed plates (corresponding to the valve seats in the
automotive example)
All this suggests that the benefits of the embossing process may indeed not
be just about reducing the gap, but may be  due to changing the nature of
the gas flow in the gap when the reed is doing its thing.
By the way another useful tip Rick Epping gave in this connection is that
one of those old microfiche readers is a great tool for examining the gaps
in a reed plate. If you come across one in a junk sale it might be
worthwhile to speculate five bucks!
Beannachtai
Aongus Mac Cana