BMW M70

BMW M70 engine
Overview
Manufacturer	BMW
Production	1987–1996
Layout
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 dual overhead camshaft (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

S70 engine

S70/2

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

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,^[12] and thus featuring 4 valves per cylinder and variable valve timing (called dual-VANOS by BMW) and individual throttle bodies. A dry sump oiling system is used. ^[13] The weight of the S70/2, plus ancillaries and full exhaust, is 265 kg (584 lb).^[14]

Applications:

• 1993–1998 McLaren F1

References

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