BMW M88 Straight-6 Engine

The BMW M88 is a straight-6 DOHC piston engine produced from 1978-1989. It is based on the M49 motorsport engine, which was used in the BMW 3.0CSi.

Design

BMW engineers used a 4-valve head and a single-row timing chain.Kugelfischer fuel injection was used with individual throttle valves and the distinctive six inlet pipes.

• Water-cooled six-cylinder in- line engine with pressure circulation lubrication
• Engine block made of cast iron with nodular graphite
• Lightweight piston from aluminum with recesses around the piston pin boss ; combustion chamber recess with valve pockets incorporated in the piston crown; three piston rings : compression ring rectangular ring , intermediate ring minute ring , oil wiper ring roof lip ring with hose spring
• Connecting rod forged from steel , connecting rod distance 144 mm
• sevenfold mounted crankshaft from forged steel with 12 counterweights and torsional vibration damper (Massetilger) at the front tailshaft
• Cylinder head made of aluminum, cross-flow cooling
• two overhead camshafts , timing chain with mechanical-hydraulic chain tensioner
• four valves per cylinder operated directly via bucket tappets ; Valves of the same function are suspended parallel next to each other, cross-flow flushing ; double, interleaved valve springs
• Intake manifold injection with rod-operated individual throttle valves , diameter of the throttle valves 46 mm, intake manifolds combined in pairs to double nozzles

• Inlet valve Ø 37 mm, valve angle 18 ° to the cylinder axis, outlet valve Ø 32 mm, valve angle 20 °
• Central, due to the slightly larger than the exhaust valves larger exhaust valves slightly spark plug position, spark plugBosch X4CS or X5DC, female thread M12 × 1.5
• Fan exhaust manifold , pipes with the same length and the same cross-section

Models

M88/1

The M88/1 was the first iteration of the M88 and was fitted to the BMW M1. It produced 277 hp (207 kW) @ 6500rpm and 239 lb·ft (324 N·m) @ 5500rpm. A dry sump is used.

Use

• Group 4, Procar
• Displacement: 3498 cm ³
• Bore: 94 mm
• Stroke: 84 mm
• Compaction 11.5: 1
• Piston speed at rated speed: 25.2 m / s
• Power: 345-361 kW (470-490 hp) at 9000 min ^-1
• Procar performance of motors: uniform 345 kW (470 hp) at 9000 min ^-1
• Torque: 390 Nm at 7000 min ^-1
• Deviations from the M88: Displacement increased to the limit of 3.5 liters, butterfly valves replaced by flat valves, valves and channel cross-sections enlarged, sharper camshafts with extended timing, forged pistons, transmission oil cooling for manual and rear axle

M88/2

For Group 5 racing, the M88 engine was turbocharged and became known as the M88/2. This race engine produced up to 900 hp (670 kW).

Use:

• 1979-1981 Group 5
• Displacement: 3191 cm ³
• Bore: 92 mm
• Stroke: 80 mm
• Compaction approx. 6,7: 1
• Performance: depending on the charge pressure of up to 625 kW (850 hp) at 9000 min ^-1
• Deviations from the M88 / 1: reduced capacity, exhaust gas turbocharging, charge pressure 1.2 to 1.4 bar. The engine and especially the supercharging largely correspond to Schnitzer developed M49 / 4 engine, which was already driven in 1976 in the 3.0 CSL race touring car of Ronnie Peterson in Group 

M88/3

The M88/1 engine was modified for use in the M635CSi and E28 M5, this engine was known as the M88/3. The Kugelfisher fuel injection was replaced with Bosch Motronic and the engine produced 286 hp (213 kW). It has a compression ratio of 10.5:1.

The M88/3 was also fitted to the South African 745i, due to packaging problems with the turbocharged M102 engine which was used in other markets.

In contrast to the M88, the M88 / 3 in the BMW M635 CSi and BMW M5 and in the BMW M745i (South Africa variant) is built in the traditional way , namely in the front - which of course is mainly because they were already in production as front-engine vehicles with rear-wheel drive ,

In order to save costs on the one hand and to simplify maintenance on the other hand, many of the tried and tested series parts were used in the design. Thus, the crankshaft with a long stroke corresponds to the 1982 built 3.5 l- M 30 , the engine block with oil supply and water pump and the crankshaft , the flywheel and the belt drive together with the ancillaries were taken from built after 1982 3.4-liter six-cylinder engine. The torsional vibration damper on the front crankshaft stump, however, had to be retuned for the higher revs of the M88 / 3.

Unlike the M88, the valve clearance is now set by shims that rest on the bucket tappet. So now the camshafts for the adjustments do not have to be removed. Otherwise, the cylinder head of the M88 / 3 does not differ in terms of constructive features from its predecessor.

The control of injection and ignition are taken over together by a Bosch Motronic. This means not only considerable cost savings due to the elimination of the equally expensive and highly precise precision mechanics of the blower injection, but also further possibilities for the efficient coordination of ignition timing and injection quantity to the respective operating state of the engine. For the detection of the load condition , a damper air flow meter is used; the puffer fish injection took its information on the load condition from the throttle position, but since there was no information about the actually sucked air flow, this is in practice rather as a targetLoad state (possible deviations of the intake air mass, eg due to clogged air filter, can not be detected in this way).

The fuel pressure in front of the injection valves is 3 bar; actually, the pressure difference to the intake manifold vacuum for all engine operating conditions is 3 bar, thus the injected fuel quantity is directly proportional to the driving time of the injectors. The injection valves are controlled electrically by the Motronic control unit.

For the S38B35 with catalytic exhaust purification , the compression was lowered to 9.8: 1, the engine thus requires unleaded fuel with an octane rating of 95 RON. In addition, shortening the camshaft opening times increased the internal exhaust gas recirculation , which reduces the raw HC emissions (emissions before catalytic converter). The engine is now equipped with an idling control valve controlled by the Motronic , with a lambda probe located in a connecting piece of the otherwise double-flow exhaust system keeping the fuel-air mixture exactly at lambda = 1 .

Use:

• from 4/84 in the model BMW M635 CSi (E24) , from 1985 in the BMW M5 (E28)
• Displacement: 3453 cm ³
• Bore: 93.4 mm
• Stroke: 84 mm
• Compaction 10.5: 1
• Piston speed at rated speed: 18.2 m / s
• Camshaft opening time 264 degrees crank angle (both camshafts are identical), camshafts driven by single row roller chain
• Power: 210 kW (286 hp) at 6500 min ^-1
• Torque: 340 Nm at 4500 min ^-1
• Others: electronic intake manifold injection and ignition ( Bosch Motronic M1.1) with air damper, wet sump lubrication, exhaust manifold, single-disc dry clutch , engine installed inclined by 30 ° to the right

• BMW M745i E23 , national version South Africa : as in South Africa because of the links transport of the exhaust-turbocharged engine of the 745i could not be installed (the steering gear of the right arm claimed the space of the turbocharger), was for this country in the M88 / 3 in the top model of the 7 Series , combined with an automatic transmission on request, installed. 

M90

The M90 engine is a lower performance SOHC engine that was based on the M88/1. It utilizes the same block from the M88 and maintains the same bore and stroke, but borrows its head from the BMW M30 engine family. Different years of M90 engines used both Bosch Motronic and Bosch L-Jetronic engine management systems. Typically identified by a white L painted on the block behind the oil filter housing and coolant water passages on the side of the block.

The M90 sold in Europe and most other markets (except North America) used a compression ratio of 9.3:1, did not have a catalytic converter and produced 160 kilowatts (210 hp).

Applications:

• 1979-1981 E12 M535i
• 1978-1982 E24 635CSi
• 1978-1982 E23 735i