1980 Chevrolet Corvette C3
The 1970 and 1980 Chevrolet Corvettes were basically the same cars with 10 years between them. The design was the same, although 1980 had a more sculpted front and rear end with less chrome. The technology was the same, and the engines looked the same on the outside. But, in 1970, the hottest Corvette had 435 hp (via Ultimate Specs).
However, in 1980, the hottest Corvette had only a modest 180 hp. It was 10 hp less in California due to more strict emission standards for that state. So, what happened in just 10 years, and where did all that horsepower go? The recession, emission standards, and safety regulations stole the performance from the legendary Corvette.