Liberty L-12

They dragged all of their test equipment.

They had a Liberty V12 on the back of a truck and they drove the thing up to the top of Pike's Peak where the air density was low and they ran a whole bunch of experiments to see if they could restore engine performance.

at altitude and they found that they could.

So all of that stuff was made available to U.S. forces in World War II, particularly for bombers, which were intended to operate at high altitude.