From IMDB Trivia:

There were three cars built for filming by the Barris Kustoms company in North Hollywood, California. All were built of steel and there were no fiberglass replicas made. Two were destroyed during filming; one in the house crash scene, the other in the barrel-roll over the police cars. The gloss-black main car was auctioned off in 1983, and assumed shipped to a European collector. All were built on a '69-'71 Continental Mark III. The stunt car, driven by' Everett Creach' had a locked 4:11 differential (to allow easier spinning), a 460 cubic-inch V8 engine, heavy-duty suspension, roll bar, safety harness, and amber-tinted glass. The top is lowered and the belt-line raised. Twelve craftsmen, led by Dennis Braid, built the main car in six weeks. There was a fourth steel car built, which was loosely put together over a late 70's Thunderbird. This car was shot out of a car-cannon for the final scene over the canyon.

In order to give "the car" a "sinister" look as requested by director Elliot Silverstein, car customizer George Barris made the car's roof three inches (7.6 cm) lower than usual and altered its side fenders that same length again both higher and longer.

The technical specifications of the four versions of "the car" were as follows. They were built on a Lincoln Mark III chassis with a 460 cubic inch engine and deep-recessed chrome-plated Cragar wheels. The 18-gauge steel frame weighed 5500 pound, was 20 ft (6 m) long and 9 1/3 ft (2.8 m) wide. The cars' bodywork was painted in steel, pearl and charcoal coloring. The cars' windows were laminated in two different shades, smoked on the inside and amber on the outside, so one could see out of it but not into it.

The distinctive sound the horn of The Car makes, spells out the letter X in Morse code. The unique tone of the car's horn is the Hadley Ambassador Rectangular Bell horn.

https://en.wikipedia.org/wiki/The_Car_(1977_film)

https://www.imdb.com/title/tt0075809/