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ⓘ Blog | BMW M70 - bmw m. The BMW M70 is a SOHC V12 petrol engine, which was BMWs first production V12 and was produced from 1987 to 1996. The BMW S702 engine, largel ..




BMW M70
                                     

BMW M70

The BMW M70 is a SOHC V12 petrol engine, which was BMWs first production V12 and was produced from 1987 to 1996.

The BMW S70/2 engine, largely unrelated to the M70 and S70B56 engines, is a DOHC V12 petrol engine, which powered the 1993 to 1998 McLaren F1.

                                     

1. Design

The M70s design is similar to that of two 2.5 L M20 straight-six engines joined at a 60 degree angle, due to the following features: single overhead camshaft valvetrain, bore spacing of 91 mm 3.6 in, bore of 84 mm 3.31 in, stroke of 75 mm 2.95 in, and a compression ratio of 8.8:1.

The M70 has the following differences with the M20 engine:

  • Hydraulic valve lifters instead of mechanically adjusted tappets, to reduce servicing requirements.
  • Electronic Throttle Control instead of a mechanical throttle cable.
  • Airflow measurement using Mass air flow sensors MAFs instead of Air flow meters AFMs to improve fuel economy.
  • A timing chain was used instead of a timing belt, to reduce servicing requirements.
  • Aluminium alloy engine block AluSil instead of cast-iron both engines have an aluminium cylinder head, to reduce weight.

The M70 has two Motronic 1.7 ECUs one for each cylinder bank. To provide redundancy, the M70 also has two fuel pumps, fuel rails, distributors, mass air flow sensors, crankshaft position sensors, coolant temperature sensors and throttle bodies.

Some M70 engines such as fitted to the E32 750iL Highline are fitted with two alternators. The second alternator is smaller and is used to charge an auxiliary battery and power equipment in the rear passenger compartment, such as a telephone, fax machine, wine cooler, independent climate control and power sun shields.

                                     

2. Versions

  • S70/3 specifications are for the race car with twin 32.9 MM air restrictors, as required by 24 Hours of Le Mans rules at the time.

M70B50

Applications:

  • 1989–1994 E31 850i/850Ci - this was mated to either the automatic ZF 4HP24 transmission or the optional Getrag 560G
  • 1987–1994 E32 750i/750iL - this was mated exclusively to an automatic ZF 4HP24 transmission
                                     

3. S70 engine

S70B56

The first engine to use the S70 name is a 5.576 cc 340.3 cu in variant of the M70 engine fitted only to the E31 850CSi. With 1.510 units produced, this is the lowest production BMW engine to date.

Three prototype dual overhead camshaft S70 engines were constructed, prior to the decision to not produce an E31 M8 model.

Applications:

  • 1992–1996 E31 850CSi

S70/2

The S70/2, while sharing the same 12 cylinder layout, bore spacing and design principle as the S70B56, is essentially a new design with the heads based on the European market S50, and thus featuring 4 valves per cylinder and variable valve timing called double-VANOS by BMW and individual throttle bodies. A dry sump oiling system is used. The weight of the S70/2, plus ancillaries and full exhaust, is 265 kg 584 lb.

Applications:

  • 1993–1998 McLaren F1

S70/3

The S70/3 is a racing engine based on the S70/2.

Applications

  • 2000 BMW X5 LM racing car
  • 1998–1999 BMW V12 LM racing car
  • 1999–2000 BMW V12 LMR racing car