(Sometimes, Christofferson).
Christoffersen is an aviation company in Oakland, CA.

-In 1915, they built six-cylinder inline engines that gave 120 hp at 1,400 rpm.

"Cristoffersen cross section"

-The cylinders were in pairs, a formula similar to that used by Mercedes, etc. It had overhead valves.

-Striking is the long loop run for the intake manifold on the engine in the photograph.

"Christoffersen 120 hp picture"

-The engine that gave 120 hp at 1,400 rpm had a displacement of 638 cu. in. It states that using these engines' cylinders they made a 12-cylinder Vee engine that gave 240 hp.