Editing Muscle car (section)

=== 1970s: Decline of the segment ===
The popularity of muscle cars declined through the early and mid-1970s due to a combination of power-sapping emissions controls and a switch to unleaded fuel mandated by the Clean Air Act, the [[1970s energy crisis]], and increased insurance costs for performance cars.<ref>{{cite book |url= https://books.google.com/books?id=J_a1AAAAIAAJ&q=The+muscle+car+business+boomed+until+shifting+social+attitudes,+crippling+insurance+rates,+the+Clean+Air+Act+and+the |page=97 |first=Brock W. |last=Yates |title=The decline and fall of the American automobile industry |publisher=Empire Books |year=1983 |isbn= 978-0-88015-004-0}}</ref> The [[1973 oil crisis]] notably resulted in rationing of fuel and sustained higher prices, which quickly made muscle cars unaffordable and impractical for many people.<ref>{{cite book|url= https://books.google.com/books?id=U9fjwQOR_5QC&q=Decline+of+Muscle+cars&pg=PA12 |title=Muscle Cars |first=Katharine |last=Bailey |year=2006 |publisher=Crabtree Publishing |page=12 |isbn= 978-0-7787-3010-1}}</ref> 

Before the Clean Air Act of 1970, a majority of muscle cars came optioned with [[Compression ratio|high-compression]] engines (some engines were as high as 11:1), which required high-octane fuel. Prior to 1970, 100-octane fuel was common. However, following the passage of the Clean Air Act of 1970, [[octane]] ratings were lowered to 91 (due in part to the removal of [[tetraethyllead|lead]]). Manufacturers reduced the compression ratio of engines, resulting in reduced performance. Simultaneously, efforts to combat [[air pollution]] focused Detroit's attention on [[vehicle emissions control|emissions control]] rather than increased power outputs.  

With performance drained, MPG mattering, and raised insurance rates, the handwriting had already been on the wall in Detroit by the early 1970s; when Ford introduced a much-downsized base inline 4-cylinder powered [[Mustang II]] in 1974, which did not even have a V8 option, the harbinger of an end to an era had arrived.