<p>James Tharp, sales manager at Fiat of South Atlanta in Morrow, Ga., poses with new Fiats on May 8. Back when gas was cheap, Americans bought cars with V-8 engines like the Big Block, Cobra Jet and Ramcharger, but now, thanks to government regulation and gas-price gyrations, the motors that move the nation's cars and trucks are shrinking.</p>

June 15, 2012