Heaviest American passenger car ever made?
1960 Lincoln Continental convertible .. tipping scales at 5712 lbs, alleged to be the heaviest produced in America by an American manufacturer. 430 cubic inch V8-2V, 315 HP (gross)
The alleged world heavyweight 'from the factory" passenger car? The late 1930s-eaerly 1940's Mercedes 770.
Most infamous for its official "governmental" usages in Germany in WWII, last years powered by 468 cu. in V8, twin-supercharged, asserted to be able to move this 10,500 lb car (it was armored) at almost 120 mph.
Mercedes 770 may have been built in a factory, but it was hardly a mass-production piece, so it probably doesn't really count if you cant order one as an ordinary citizen.
Example, the "Beast" may weigh up to 20K lbs, plus may even be on a "truck" chassis. 6.6L V8 of unknown power can only move the Beast of 60 mph (alleged)
source:
Here Are The US Presidential Limos That Have Served From FDR To Trump