BMW’s plug-in hybrid sports car will soon receive a few upgrades. The changes include a new rear glass panel with slotted air vents that will help hot air escape from the mid-mounted turbocharged 1.5-liter three-cylinder gasoline engine. In addition, a more robust battery pack is designed to provide added electric-only distance that currently tops out at just 15 miles. This will also result in an increase in net output to an estimated 400-plus horsepower from the current 362. Suspension modifications are also planned, but the big news is the availability of an i8 convertible, complete with a power-retractable roof. Expected timing for the revised 2018 i8 and the convertible’s arrival is the third quarter of 2017.