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 solidified himself as a full-time starter, culminating in 1984 when he secured the lowest ERA title with a 2.48 average and set a league record for most shutouts with four.