Don't do it unless you buy a 25" leg motor to replace your 20" leg outboard. I just raised my transom to suit a 25" leg. My buddy did the same to a Hourston and it definitely helps with water coming into the transom well, and with saltwater splashing onto the motor. But if you are planning on keeping your 20" leg, don't do it! Your prop can't be 5" higher than it was if that is what you are asking.