Complex sentence: In the early 20th century, automotive engines were limited in terms of revolutions per minute (rpm), to the tune of about 3,000 rpm, which meant that the easiest way to increase the power output of an engine was to increase its displacement.
Split into simpler sentences: In the early 20th century, automotive engines were fairly limited in terms of revolutions per minute (rpm), with 3,000 rpm constituting an upper limit. This meant that the easiest way to increase the power output of an engine was to increase its displacement.