Re: alfa-digest V7 #1156 Spica "Improvements"

[Scott Fisher <sefisher@domain.elided>]

Grinch writes:

> I have a sincere request regarding the oft-mentioned post-production
> "improvements" to the Spica fuel distribution pump attributed to Wes
> Ingram (and others).

I can't find any reference in #1156 nor the several digests at either
side, and neither in my own comments nor in anyone else's, to
"improvements" to the Spica.  There has been discussion (some of it
mine) about modifications to Spica pumps to account for increased engine
airflow due to changes in the ports, cam timing, etc., in a way
analogous to changing the chokes, jets, emulsion tubes etc. of a Weber. 
That doesn't suggest improvements to me, merely compensatory
modifications to synchronize with others elsewhere in the system.

I'd like to second the request for details about altering the Spica pump
to flow more gasoline in concert with increased airflow.  A little
reflection suggests that the extra fuel required, even given fairly
dramatic airflow increases, need not be all that high (especially so
since the air:fuel ratio is measured by mass, not by volume, so simply
dividing the increased CFM by 14.6 is the wrong thing to do).  This
further suggests that any such changes must be made with great
precision.  (As well as accuracy -- two very different characteristics,
as I think I've demonstrated sufficiently in recent days...)

On a more general note: What is the canonical reference for someone who
wants to learn all there is to know about Spica?  The owner's manual for
my '74 gives a diagram of the external components, tells me to move the
temperature compensator to C when temperatures fall below 59 degrees F
and to F when they fall below 32 degrees F, and it tells me to change
the pump's internal oil filter every 12000 miles.  It shows how filtered
air, at idle, is delivered through rubber hoses to the individual
throttle bodies, and it shows how to time the pulley to the crankshaft
when replacing the drive belt.  But it doesn't say, for example, how the
Spica measures intake air mass and meters the precise *and* accurate
amount of fuel for each intake stroke of each cylinder individually, at
all throttle positions and all RPM from 800 to 6500.  I'd like to do my
homework with the right material.

Or should I just keep to the time-honored Internet tactic of posting the
wrong information so that those who know will provide the right answers?
:-)  ("The Spica pump senses intake air by measuring the oscillations in
a substance made of egg yolks and almond paste, which must be renewed
every 5000 km...")

> I would appreciate receiving detailed definitions and descriptions
> with documentation of these "improvements" from anyone involved so
> I can pass them along to Dario Radaelli (the developer of the 
> system) for his comments.

I'm sure many of us would like you to convey our appreciation for his
contributions.  I stand by my statement in #1156 that it's a
magnificent, elegant system, and would add to those characteristics that
of robustness, which lets me enjoy it 25 years later.

- --Scott Fisher

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End of alfa-digest V7 #1159
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