Yet the BMW M4 convertible is a slightly troubling device for purists. The M4 reason to exist is the exist is the exhilaratingly tactile pleasure of driving it as rapidly as you dare. That why the M4 coupe has a 431 hp turbocharged straight-six,hippopotamus fat rubber,a front bumper gaping with air guzzling grilles , the option of a swift shifting seven-speed,paddle.triggered transmission and a carbon fibre roof.