BMW released powertrain and performance specifications for the 2019 BMW Z4 on Tuesday, nearly a month after revealing the new two-seat roadster at Pebble Beach. Base Z4s, dubbed the Z4 sDrive30i Roadster, will be powered by a 2.0-liter turbo-4 with 255 horsepower and 295 pound-feet of torque. The base turbo-4 is related to similar engines found in…