The Quattroporte I was made between 1963 and 1969. In total, about 730 of these models were produced. The first models had a V8 engine making 256 horsepower with a 5 speed manual or 3 speed automatic transmission. Later models, after 1968, included a larger V8 engine. There was a US model of this car that featured twin headlights, which also became a feature on later European models of the Quattroporte I.
The Quattroporte II was sold from 1974 until 1978. Citroen had purchased the company, and this car would be based on a Citroen platform and would have a Citroen SM chassis. It had a V6 engine that didn't impress anyone. Only 13 of them ended up being produced, and sever were by special order.
The Quattroporte III was sold from 1976 through 1979 as the 4porte, and from 1979 to 1990 as the Quattroporte. It now had a more luxury-inspired , business-oriented design than before. It was now competing with Mercedes Benz instead of Ferrari or Lamborghini. About 2,141 Quattroporte IIIs were produced, with over 1,800 more 4portes made in those early years. All of them got a V8 engine, although there were several different variations of that engine.
The Quattroporte IV was made from 1994 through 2000. It was designed by Marcello Gandini, the same man who designed the Lamborghini Countach. Although a biturbo V6 was the standard engine, it was a light car with a low drag coefficient, so performance numbers were still quite good.
These cars are still quite popular with collectors, especially the rarer ones. Look for them to appreciate in value in the coming decades. You can still find some listed on eBay, if you are looking to buy.