The Ruf CTR (Group C, Turbo Ruf) also known as the CTR Yellowbird or simply Yellowbird, is a limited-production, high performance sports car manufactured by German automobile manufacturer Ruf Automobile. Introduced for the 1987 model year and based on the Porsche 911, the CTR featured an enlarged and highly tuned version of Porsche's 3.2 litre flat-six cylinder engine, lightened body panels, an integrated roll cage (adding chassis stiffness in addition to occupant safety), upgraded suspension and braking systems, a custom-designed transmission, and several unique trim pieces such as polyurethane bumpers, and the use of the side-mounted oil filler (a Porsche feature for the 1972 model year only) necessitated by relocating the oil tank forward to clear the intercooler on that side.