This is an original US made (under license), 1918 Hispano-Suiza engine.  Earlier Jennies had Curtiss built OX-5 engines with an output of 90 horsepower.  This Hisso produced 150 horsepower. One other model in 1918 produced 180 horsepower.  Notice the valve and rocker arm covers, not common for this period.  The reason is this engine has overhead cams requiring positive pressure lubrication and protection from the elements.  The cams are driven by shafts and gears at the rear of the block.  Also note the single unit casting of four cylinders, water jackets and heads, a phenomenal piece of craftsmanship.  On each side of the cylinders you can see the dual spark plugs.  The tubes running from the block to the top of the heads is for the cams' oil supply.  If you look closely, you can see the four brass priming valves on the air intake runners.  The pilot used used them for dribbling a small amount of gasoline into the engine for cold starting.  Few carburetors had chokes then.  The block is a two piece cast aluminum unit.