Straight hitters looking for more distance often try to increase their turn.
If so, you're on the right track. But if those extra yards aren't appearing, then your turn isn't getting any bigger, despite your efforts. Chances are you're only increasing the tilting of your shoulders in the backswing, which leads to a choppy downswing and weak slices. You'll find it easier to make a full turn if you allow the clubface to fan open during the backswing. Try this experiment and you'll understand why.