How many valve reliefs are in D15B6 pistons? Q: Why does anyone care? A: If you're going to swap the head on an HF engine to a 16 valve D series head, you might need a set of pistons with 4 valve reliefs each. So here we go- courtesy of ryan89crx, who pulled the head on his 89 CRX HF just to see how many valve reliefs he had in his pistons. There are only 2 reliefs per piston. Thanks Ryan!