Need HP/Torque Curve for Honda D16Y5 Engine

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

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.

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.