# BMW 8 Series (E31)

The BMW E31 is the first generation of the BMW 8 Series. It is a grand tourer built by BMW from 1990 to 1999 as a 2-door coupé, powered by either a V8 or V12 engine. Whilst it did supplant the original E24 based 6 Series in 1990, it was not a direct successor, but a new model class with a substantially higher price and performance than the 6 Series.

## Development

Development of the 8 Series began in July 1981, with the design phase reaching completion in 1986, although the launch was delayed due to still-strong 6 Series sales. The 8 Series debuted at the Frankfurt Motor Show (IAA) in early September 1989. The 8 Series was designed to move beyond the market of the original 6 Series. The 8 Series had substantially improved performance, as well as a far higher purchase price.
Over 1.5 billion Deutsche Marks were spent on total development (2019 USD nearly $900 million). BMW used CAD tools, still unusual at the time, to design the car's all-new body. Combined with wind tunnel testing, the resulting car had a drag coefficient of Cd=0.29, a major improvement from the previous BMW M6/635CSi's 0.39.
The 8 Series offered the first V12 engine mated to a 6-speed manual transmission on a road car. It was one of the first vehicles to be fitted with an electronic drive-by-wire throttle. The 8 Series was one of BMW's first cars, together with the Z1, to use a multi-link rear axle.
CAD modelling allowed the 8 Series unibody to be 3 kg (6.6 lb) lighter than that of the preceding 6 Series (E24). However the production 8 Series was significantly heavier when completed due to the large engine and added luxury items—a source of criticism from those who wanted BMW to concentrate on the driving experience. Some of the car's weight may have been due to its pillar-less "hardtop" body style which lacked a "B" pillar.

## Sales

Sales of the 8 Series were affected by the global recession of the early 1990s, the Persian Gulf War, and energy price spikes. As a result, plans for the high performance M8 variant were dropped in 1991.
BMW pulled the 8 Series from the North American market in 1997, having sold 6,920 cars. BMW continued production for other markets until 1999 having sold 30,609 in all markets. The base price for an entry-level 8 series in the early 1990s started in the US$70,000 range, which is US$163,250 in 2023.

## Models

The production totals for each model are:
* 840Ci with the M60 engine: 4,728
* 840Ci with the M62 engine: 3,075
* 850i / 850Ci with the M70 engine: 20,072
* 850Ci with the M73 engine: 1,218
* 850CSi with the S70 engine: 1,510

### 840Ci

The 840Ci was offered with two different engines. The first used the 4.0-litre M60B40 V8 engine having a power output of 210 kW (286 PS) and was produced from mid-1993 to late 1995. From mid-1995, production phased in the newer 4.4-litre M62B44 V8 engine, which had better fuel economy and more torque, though power output remained unchanged.
The 840Ci was available with a 5-speed automatic transmission, though European cars were given the option of a 6-speed manual transmission. The only external features distinguishing the V8 model from the V12 models were the quad round exhausts, which were square in the V12 models. The 840Ci stayed in production until May 1999.

### 850i/Ci

The 850i was the first model of the 8 Series launched in 1990 with the 5.0-litre M70B50 V12 engine having a power output of 220 kW (300 PS). It was available with either a 4-speed automatic or a 6-speed manual gearbox.
Around the time of the introduction of the 840Ci in Autumn 1993, the 850i was renamed the 850Ci. From October 1994, BMW installed the new M73B54 V12 engine in the 850Ci, the new engine being from the newly launched E38 750i. Thus, cars with 850Ci badging used both the M70 and M73 engines, with those built before 10/94 using the older E32-type M70. As the displacement of the M73 increased to 5.4-litres and the compression ratio went up, the power output increased to 240 kW (326 PS).

### 850CSi

As a top-of-the-range variant of the 8 Series, the 850CSi took over from the prototype M8 variant. The 850CSi used the same engine as the 850i, which was tuned so significantly that BMW assigned it a new engine code: S70B56. The modifications included Bosch Motronic 1.7 fuel injection, a capacity increase to 5,576 cc (5.6 L) and power increase to 280 kW (381 PS) at 5,300 rpm and 550 N⋅m (406 lbf⋅ft) of torque at 4,000 rpm. Road & Track recorded a 0–60 mph (0–97 km/h) time for the 850CSi of 5.9 seconds.
The 850CSi's modified suspension included stiffer springs and dampers that reduced the car's ride height. The recirculating ball steering ratio was dropped 15% over the standard E31 setup. The model also sported staggered throwing star wheels. The front and rear bumpers were reshaped for improved aerodynamic performance. Four round stainless steel exhaust tips replaced the square tips found on other models. The 6-speed manual gearbox was the only transmission option. In Europe, all 850CSi's came with four-wheel steering (AHK - Aktive Hinterachs-Kinematik, Active rear axle Kinematics), upgraded and ventilated brakes with floating front discs, rear differential oil cooler, engine oil cooler, two-tone interior, sports seats, and reshaped mirrors. In the United States, the cars instead received "BMW Motorsport" writing on the doorhandles.
Production ended in late 1996 because the S70 engine could not be modified to comply with new emission regulations without substantial re-engineering.

### Other models

Alpina produced two 8 Series variants, the B12 5.0 and the B12 5.7. There have also been aftermarket conversions to change it to a drop-top convertible.

## Engines

| Model | Years | Engine | Power | Torque |
| 840Ci | 1992–96 | 4.0 L M60 V8 engine | 210 kW (286 PS; 282 hp) | 400 N⋅m (295 lbf⋅ft) |
| 840Ci | 1995–99 | 4.4 L M62 V8 engine | 210 kW (286 PS; 282 hp) | 420 N⋅m (310 lbf⋅ft) |
| 850i, 850Ci | 1990–94 | 5.0 L M70 V12 engine | 220 kW (300 PS; 296 hp) | 450 N⋅m (332 lbf⋅ft) |
| 850Ci | 1992–99 | 5.4 L M73 V12 engine | 240 kW (326 PS; 322 hp) | 490 N⋅m (361 lbf⋅ft) |
| 850CSi | 1992–96 | 5.6 L S70 V12 engine | 280 kW (381 PS; 375 hp) | 550 N⋅m (406 lbf⋅ft) |
2017 United States Environmental Protection Agency estimates for cars equipped with automatic transmission:
* 840Ci:
       Fuel type: Premium
       city: 14 miles per US gallon (17 L/100 km; 17 mpg$_{‑imp}$)
       highway: 19 miles per US gallon (12 L/100 km; 23 mpg$_{‑imp}$)
       combined: 15 miles per US gallon (16 L/100 km; 18 mpg$_{‑imp}$)
* 850Ci:
       Fuel type: Premium
       city: 12 miles per US gallon (20 L/100 km; 14 mpg$_{‑imp}$)
       highway: 19 miles per US gallon (12 L/100 km; 23 mpg$_{‑imp}$)
       combined: 15 miles per US gallon (16 L/100 km; 18 mpg$_{‑imp}$)

## Transmissions

The 840Ci (4.0/4.4 L V8) models were equipped with a 5-speed automatic transmission or a 6-speed manual transmission. The 850i/850Ci (V12) models each use either a 4-speed automatic transmission or a 6-speed manual transmission, a 5-speed automatic transmission was fitted from mid-1994. The high performance 850CSi model only came with a 6-speed manual transmission.

## Prototype models
### 830i

The 830i was a prototype that did not reach production. As the potential entry-level model, the 830i was to use the 3-litre V8 with 160 kW (215 hp) from the 530i and 730i, known internally as the M60B30. Eighteen cars were produced, thirteen of which had an automatic gearbox fitted. The model was dropped in favour of the 840Ci and almost all of the 18 cars were dismantled; one car is in a BMW museum.

### 850i Cabrio

The 8 Series had been planned from the start with a convertible version in mind. Although the 850i Cabrio was developed to production readiness, it never went into production. At a relatively late date it was decided that this model was unlikely to recover the cost of putting it into production. A prototype in red resides in the BMW Museum in Munich.

### M8

The M8 was originally envisioned as a Ferrari competitor equipped with a special version of the S70 engine, with modifications including a displacement increase to 6064 cc, dual overhead camshafts for each cylinder bank, individual throttle bodies with roller valves, four valves per cylinder, carbon fibre intake manifolds and continuously variable valve timing. As a result, it was estimated the M8 would achieve a top speed of 320 km/h (199 mph), power output is 471 kW (640 PS) and its torque is 650 N⋅m (479 lbf⋅ft). A common misconception is that this engine powered the McLaren F1. The S70/2 used in the McLaren F1 was not based on the prototype 48-valve V12 used in the M8, and was a completely new design.
The car was given two intakes by its rear arches for engine and differential oil cooling. It was also given a wider track via a wider drive axle as well as uprated front brakes. The interior was completely stripped, with bucket seats and additional gauges for oil pressure, oil temperature, and water temperature. The M8 was given a B-pillar to retain structural rigidity as well as having its pop up headlights deleted from the car.
Other modifications include bodywork modifications such as a new front bumper, new wing mirrors, more flared wheel arches and a vent in the bonnet. The car's kerb weight was reduced to less than 1450 kilograms by making elements of the car glass reinforced plastic (such as the bonnet, doors and boot lid), using carbon fibre wheels and removing the rear seats from the car. The windows were made of Lexan. The oil reservoir was moved to the trunk of the car; oil pipes went through the roof of the car.
The project was eventually scrapped because BMW decided that there was no market for a high performance variant of the 8 Series primarily because of the on-going economic recession of the 1990s. The only prototype ever produced (one that was reportedly not even safe for normal road usage) was locked away by BMW in the company's Giftschrank (poison storage). BMW and the M Division had strongly denied that the car was even a possibility since the initial stages of its development. A world exclusive feature in the February 2010 issue of BMW Car Magazine, however, revealed that the M8 prototype still exists in its entirety. The car was unveiled to journalists for the first time on July 2, 2010, at the BMW Museum in Munich. The only public showing of the car happened on August 17, 2012, during 'The Legends of the Autobahn' car show held in Carmel, California. The car was specially shipped from Germany for the appearance.
Although the M8 was never produced, the 850CSi was also tuned by BMW's M division. Aside from sporting an M-tuned engine (as identified by the S prefix (which a non-M tuned engine would bear) instead of the M prefix), the car's VIN identifies the car as being built by BMW Motorsport (a WBS prefix) instead of BMW AG (WBA prefix). Per BMW's own protocol, the 850CSi as marketed was essentially a de-tuned version of the putative M8.

## Alpina models
### B12 5.0

The B12 5.0 was built from 1990 to 1994 based on the BMW E31 850i with an Alpina-modified BMW M70 V12 (shared with the E32 B12 5.0) producing 257 kW (350 hp) and mated to an automatic transmission.

### B12 5.7

The B12 5.7 was available from 1992, based on the BMW 850CSi with the BMW S70B56 V12 engine bored out to 5.7 litres along with a modified intake, crankshaft, camshafts and a stainless steel exhaust system as well as a 6-speed manual gearbox. The modified engine produced 306 kW (416 hp). The carbon-fibre bonnet had cooling vents and a NACA duct for improved engine cooling. Performance figures included a 0–60 mph (0–97 km/h) acceleration time of 5.8 seconds and a top speed of 300 km/h (186 mph).
* Alpina B12 5.0 Coupé
* Alpina B12 5.7 Coupé

## Motorsport

The 8 Series is a very rare car to see in any form of motorsport. One of the most successful examples was built by Wagenstetter Motorsport however, and, until recently, was raced in the VLN Nürburgring endurance championship. It is based on an 840i, but now has an E39 M5 5.0-litre V8, which has 414 kW (555 hp) and 472 lb⋅ft (640 N⋅m) torque, and a six-speed gearbox from the same car.