The Bovensiepen Spider is based on a BMW Z4 and comes from a company run by the family that originally founded Alpina.The turbo 3.0-liter inline-six now produces 429 horsepower and 427 pound-feet of torque, up by 47 hp and 59 pound-feet.The Spider also wears revised bodywork and has fancier leather inside. Only 99 units will be built.