BMW M70

BMW M70 engine
Overview
Manufacturer	BMW
Production	1987–1996
Combustion chamber
Configuration	SOHC 60° V12
Chronology
Predecessor	None
Successor	BMW M73

The BMW M70 is a V12 SOHC petrol engine, which was BMW's first production V12^[1] and was produced from 1987 to 1996.

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

Design

The M70's design is similar to that of two 2.5 L M20 straight-six engines joined at a 60 degree angle,^[2] due to the following features: SOHC valvetrain, 91 mm (3.6 in) bore spacing, 84 mm (3.3 in) bore, 75 mm (3.0 in) stroke and 8.8:1 compression ratio.^[3]

The M70 has the following differences with the M20 engine:

• Aluminium alloy engine block - with AluSil liners - instead of cast-iron (both engines have an aluminium cylinder head), to reduce weight.^[4]
• Airflow measurement using Mass air flow sensors (MAFs)^[5] instead of Air flow meters (AFMs) to improve fuel economy.
• Electronic Throttle Control instead of a mechanical throttle cable.
• A timing chain was used instead of a timing belt,^[6] to reduce servicing requirements.
• Hydraulic valve lifters instead of mechanically adjusted tappets, to reduce servicing requirements.

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.^[7]

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.^[8]

Models

M70B50

Applications:

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

S70 engine

BMW S70/2 engine
Overview
Manufacturer	BMW
Production	1993–1998
Combustion chamber
Configuration	DOHC 60° V12
Chronology
Predecessor	None
Successor	None

S70B56

The first engine to use the S70 name is a 5,576 cc (340 cu in) variant of the M70 engine fitted only to the E31 850CSi.^[9] With 1,510 units produced, this is the lowest production BMW engine to date.^[10]

Three prototype DOHC S70 engines with four valves per cylinder were constructed, prior to the decision to not produce an E31 M8 model.^[11]

Applications:

• 1992–1996 E31 850CSi

S70/2

The S70/2, while sharing the same 12 cylinder layout and design principle as the S70B56, is essentially two European market S50s joined together, and thus features 4 valves per cylinder and variable valve timing (called dual-VANOS by BMW) and individual throttle bodies. A dry sump oiling system is used. ^[12] The weight of the S70/2, plus ancillaries and full exhaust, is 265 kg (584 lb).^[13]

Applications:

• 1993–1998 McLaren F1

S70/3

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

Applications

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

References

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