Pena became a full-time starting pitcher in 1983 and 1984, winning the ERA title in 1984 with 2.48 earned run average and leading the league with four shutouts.
In 1983 and 1984, Pena transitioned to being a full-time starter, achieving dominance in 1984 by securing the lowest ERA title with a 2.48 average and setting a league record for most shutouts with four.