[sharkbite]

Assuming you can get the water to turn to steam (most steam engine run between 400-500 degrees, and an internal combustion engine is designed to be kept much cooler than this)....

and assuming since you are talking a 6-pot its probably a 4 -stroke?


I'm guessing it would work something like this:

forget spraying water with injectors - there ain't enough heat in the
cylinder without some internal combustion to turn it to steam

Air inlet valves would need to be open for the entire power stroke, to admit
high pressure steam, potentially generated from wrapping the pipes
around the exhaust as previously suggested.
they'd have to be closed for the entire exhaust or "up" stroke.

Outlet valves would need to be closed for the entire down stroke (or "power" stroke) and open for the entire up stroke to exhaust the steam properly.

You would need find a way to delete the compression stroke entirely (all valves closed on an up stroke)

You'd need a separate manifold for the 3 "steam" cylinders so that the spent steam does not cool the exhaust from the proper engine.

Steam engine pistons are "pushed" by steam from first one end, and then the other
to maximise the time that they are providing force to the crank.

you wouldn't be able to do this in a 4-stroke, as the bottom end has no means to control the steam.