Miata Mailing List: May 1994, Message #57
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   From: jwa@yog-sothoth.dcrt.nih.gov (James W. Adams)
Subject: Weber DCOE update
   Date: Tue, 3 May 1994 11:39:23 -0400

So far, Milton has suggested HKS.  I will try to call them in the next
day or so.

This seems a great way to _really_ open up the intake on the Miata if
you aren't subject to Draconian inspections, or for off-road use. It
retains the classic flavor and character of the car, while providing a
significant performance optimization for the naturally-aspirated,
free-revving engine.  Using venturies sized equal to the intake valve
ports in the head (anyone know the intake valve _port_ inside diameter?
the specs only list valve head diameter), the intake will be essentially
wide open at full throttle, more than doubling the present throttle
area.  At these dimensions, Webers can be tuned to provide drivability
nearly equal to the stock FI.  You can get a few extra CFM by using the
shortest velocity stacks inside a K&N filter body.

If you retain the catalyst, CO and tailpipe HC may even remain legal,
though NOx will not, mainly due to increased peak combustion temp (and
greater volumetric efficiency) and lack of feedback mixture control for
the reduction catalyst.  Milton also mentioned that HKS may have a
"sports" FI under development, which would presumably offer similar
performance with the possibility of full emissions compliance. 
Unfortunately, the cost of such a setup is bound to be significantly
higher than a dual DCOE setup, which will probably run somewhere between
$700 to $1,200, depending on how much work you are willing/equipped to
do yourself.

For those without the joy of the Weber experience, :)  Weber DCOs, and
similar carbs such as Dellorto, are designed to work in venturi per
cylinder, non-plenum applications where the A/F mixture frequently
passes through the carb several times due to the violent pressure waves
generated by valve closure transitions.  This permits use of an enormous
throttle/venturi area compared to a "conventional" single carburetor on
a plenum manifold, without any sacrifice in drivability or throttle
response.  The DCOE was developed for 1930s Formula One cars, and thus
*all* internal parts are replaceable to calibrate the performance, the
only exception being the throttle body itself.  Even the venturis can be
changed.  Unfortunately, choosing the correct internal parts,
particularly the emulsion tubes, is something of a Black Art which only
experience can teach, particularly since documentation is quite
inscrutable and the numbering system for the emulsion tubes follows no
meaningful pattern.  It's frequently best to start from a configuration
for a similar application which is known to run well.  Fortunately, the
popularity on 4-cyl, small-displacement engines provides many such
examples.