For 1973, the vent wing windows were deleted from the Scamp, and all models were given a new grille and front bumpers able to withstand damage at a 5 mph (8.0 km/h) impact, as well as steel beams inside the doors to protect vehicle occupants in side-impact collisions as mandated by NHTSA. The door beams, the new bumpers and their impact-absorbing mounts, a rubber-booted telescoping system attached to the car's structure, added mass to the Valiant. At the same time, engines were being progressively detuned to comply with increasingly stringent emissions regulations. Performance and economy suffered as a result.
Source: Wikipedia, 2013