If it’s too loud for you, you’re too old. Rafael Capone, a car customizer and sound engineer from Atlanta, Georgia, is the proud owner of the world’s loudest Hummer, which he’s dubbed Soul Asylum H2.

A tall, white Nissan Terra rolled into Lucas Oil Raceway, commanding the eyes and ears of everyone nearby. Its engine, burning against a blistering hot June afternoon, buzzed steadily, standing atop a ...