Is it the manual or automatic transmission? What year? Which sub-model... it matters for understanding your car's potential.
__________________
See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.
There were even some Euro-spec Civics with a 2.0L Rover Diesel engine in the 90s, and other versions with that Isuzu-designed 1.7L 4EE2 turbodiesel widely used by GM in overseas markets.