The e31 8 series was introduced in 1989, and was supposed to replace the 6 series which had been in production from 1976 until 1989.
The only model available at that time was an 850i, with a 12 cylinder engine providing 300HP, and was at least 50% more expensive then the 6 series.
So why did BMW make the 8 series? Mercedes came on the market with the 500SL, and BMW had to have a competitor.
Problem with this was that it wasn't in BMW's lane; BMW buyers couldn't afford it, nor the fuel cost, and went for the 5 series instead.
This 2 door coupé had a top speed of 250km/h, and was replaced by the 850Ci in 1993.
At the same time the 840Ci and the 850CSi were introduced. The 840ci received an 8 cylinder engine with 286HP.
The 850CSi (top model) had a 12 cylinder engine providing no less then 380HP, and had a special M package with M rims and mirrors.
In 1994 the 850i got an engine tune-up and now had 326HP, and in 1996 the 840Ci received an engine tune-up.
The 8 series was in production until 1999, the 850CSi only lasted until 1997.