The 964 was considered to be 85% new as compared to its predecessor, the Carrera 3.2. The first 964s available in 1989 were all wheel drive equipped "Carrera 4" models; Porsche added the rear wheel drive Carrera 2 variant to the range in 1990. Both variants were available as a coupé, Targa or Cabriolet. The 964 Carrera was the last generation sold with the traditional removable Targa roof until the 2011 991 (993, 996, and 997 versions used instead a complex glass-roof "greenhouse" system). A new naturally aspirated engine called the M64 was used for 964 models, with a flat-6displacement of 3.6 litres. Porsche substantially revised the suspension, replacing torsion bars with coil springs and shock absorbers.[4] Power steering and ABS brakes were added to the 911 for the first time; both were standard. The exterior bumpers and fog lamps became flush with the car for better aerodynamics. A new electric rear spoiler raised at speeds above 50 mph (80 km/h) and lowered down flush with the rear engine lid at lower speeds. A revised interior featured standard dual airbags beginning in late 1989 for all North American production 1990 MY cars. A new automatic climate control system provided improved heating and cooling. Revised instrumentation housed a large set of warning lights that were tied into the car's central warning system, alerting the driver to a possible problem or malfunction.