Drain pineapple, reserving 3/4 cup juice; set pineapple aside. In a small saucepan, combine the cornstarch, curry powder, salt, pepper and reserved pineapple juice until smooth. Bring to a boil; cook and stir for 1 minute or until thickened. Remove from the heat; cool to room temperature. Stir in mayonnaise and sour cream.
In a large bowl, combine the shrimp, pasta, water chestnuts, red pepper and reserved pineapple. Add dressing and toss to coat. Cover and refrigerate for at least 2 hours before serving.