The 1975 model was advertised as "a more efficient Corvette," as service intervals were extended and electronic ignition and the federally mandated catalytic converter were introduced with "unleaded fuel only" warnings on the fuel gauge and filler door. Dual exhaust pipes were routed to a single converter, then split again leading to dual mufflers and tailpipes. Starting this year, tachometers were electronically driven. The Corvette began to be influenced by the metric system as speedometers now displayed small subfaces indicating kilometers-per-hour. 75's featured revised inner bumper systems with molded front and rear simulated bumper guards. The urethane rear bumper, now in its second year, reappeared as a one-piece seamless unit. This was the final year for Astro Ventilation. Power bottomed out this year — the base engine produced only and the only remaining optional motor, the L-82, dropped an astonishing , managing to deliver . With no larger engine available, L-82 hood emblems began to appear on cars so equipped. Unchanged was the standard rear axle ratio for the base engine, which remained at 3.08 with automatic and 3.36 with manual transmission. This was the last convertible for the 1968-82 third-generation and only 12% of the cars were ordered as such. As in previous years, a folding top came standard with roadsters and a body color or vinyl covered hardtop was optional at additional cost. Anticipating further federal safety restrictions, Chevrolet believed it would be Corvette's last soft-top model ever but the convertible returned in 1986. Due to the state's strict emissions standards, this was the last year Chevrolet installed the L-82 engine in a Corvette destined for California.