i understand "free", but i'm still not sure how you'd use this motor in
this case though.  the hx motor is very finely tuned [with fuel economy
in excess of the civic hybrid] and trying to replicate this efficiency
is non-trivial.

the engine computer for this motor expects to see things like road speed
and oxygen sensor readings.  you can wire this motor to give those
readings to the ecu, but you need to know what you're about, and the
expense of custom parts to achieve this will probably exceed the cost of
a used diesel motor whose engine management is trivial and whose fuel
efficiency is a given.  using non-honda engine management on your hx
motor probably won't give you good efficiency results.

what i'd do is look for a used pump engine [from a building sprinkler
system?] or something like that.  cheap/free.  easy to manage.  no gearing.

No doubt that a diesel woul dbe the best power plant to use. I happen
to have a Civic motor that was nearly free and has less than 4k miles
on it. I do however agree with you about the Honda engine not being
very efficient down at 1800 RPM and have considered a 2:1 reduction
which I may opt for. Still would like to have some idea as to the
power curve down on the low end.

1800 won't be most efficient for that engine - probably best to use a
geared reduction or better yet, a lower revving diesel engine.

I'm looking for a HP/Torque curve for a D16Y5 (2000 Civic HX). I'm
building a power generator and need to know how much power this engine
will develop at 1800 RPM. - DoubleD