From GM press: The 1970s -- A Time of Change.
The 1970s were a time of great change for Corvette. While a late production start for the 1970 model year prevented the first cars from rolling off the assembly line until January, sales rebounded in 1971 and continued to climb. But at the same time, outside forces, such as the oil embargo and increasing government regulations, were having an impact on Corvette performance.
The original high-performance LT1 engine, a 350-cu.-in. "Small Block," was introduced in 1970. It generated 370 horsepower. That year, the "Big Block" displacement was increased to 454 cu. in., and was rated at 390 horsepower in the LS5 version.
In 1971, a special-purpose "Big Block" V8 was available that produced 425 horsepower. But 1971 was the last year for "gross" horsepower ratings. The industry changed to a "net" rating system that accounted for the exhaust system, vehicle accessories and other components. It provided a truer measure of an engine's performance and is still used today.
The Convertible model was dropped at the end of the 1975 model year. The next Corvette Convertible would not be available until 1986.
In 1977, Corvette hit the 1/2-million milestone as the 500,000th car rolled off the assembly line. Leather seats were standard for the first time, although buyers could choose cloth as a no-cost option. Production reached 49,213 units.
Corvette celebrated its 25th anniversary in 1978 and, in recognition of this event, was selected to be the Official Pace Car of the Indianapolis 500. Two special models were produced for public sale -- a Pace Car appearance edition and a special Silver Anniversary paint package.
In 1979, Corvette production hit 53,807 units -- a record that still stands today.