1975 was the last year for a convertible until 1986. It was the first year for catalytic converters as well as the first year for HEI (high energy ignition). 1975 also marks the first year since 1964 that only one engine displacement size was available. The rear "Rubber Bumper" was updated this year to be one piece, eliminating the seam down the middle. Internally both the front and rear bumpers were redesigned to improve low-speed crash survivability. The speedometer this year also included km/hr in a smaller type face than MPH in the US, in Canada it was reversed. This was the last year for "Astro Ventilation". This was the first year for the headlight warning "Buzzer". Zora Arkus-Duntov resigned from GM this year and Dave McLellan took over Corvette.