Boxster
Engine M 96/20
The engine of the Boxster is a completely new water-cooled, 6-cylinder, 4-stroke Boxer engine with the following special features:
- Four-part and vertically split "open-deck" crankcase with LOKASIL cylinder sleeves and iron-coated pistons
- Crankshaft-bearing shells made of aluminium with nodular cast iron components
- Integrated dry-sump lubrication
- Four overhead camshafts with camshaft adjustment (VarioCam)
- Four-valve technology
- Three-part cylinder head
- Hydraulic valve-clearance compensation
The most important engine data at a glance:
Displacement 2,480 cm3 (stroke 72 mm, bore 85.5 mm) - (151,3 cu.in.)
Power output 150 kW/204 HP (SAE 201 HP)
at engine speed 6,000 rpm
Max. torque 245 Nm (SAE 181 lb.ft)
at engine speed 4,500 rpm
Compression ratio 11.0 :1
Fuel grade 98 RON/88 MON (unleaded premium plus)
Engine Mounted Components:
Front Of Engine:
Image Legend:
1 Belt pulley
2 Power steering pump
3 Alternator
4 Oil return pump for cyl. head line 4-6
5 Coolant pump
6 Coolant duct case
7 Engine temperature sensor
8 Belt tensioner
9 TDC mark
10 Front engine mount
11 Ignition coils
12 Pressure regulator
Rear Of Engine:
Image Legend:
13 Starter ring gear
14 Oil-to-water heat exchanger
15 Oil return pump for cyl. head line 1-3
16 Engine speed and reference mark sensor
17 Oil filter housing
18 VarioCam valve
19 Tank venting valve
20 Throttle potentiometer
21 Ignition coils
22 Oil separator
23 Starter housing
24 Exhaust manifold
Cross Section of Engine:
Cross Section Of Engine:
Full-load Curve M 96/20:
Full-Load Curves:
Crankcase:
The crankcase comprises the two crankcase halves as well as the vertically split (along center of crankcase) bearing case. The bearing case is made of aluminium, but 7 bearing shells are made of nodular cast iron (see arrows).
This construction means that changes in the bearing clearance resulting from thermal fluctuations are reduced by a considerable degree which, in turn, reduces mechanical noise. An additional benefit is that, when the engine is warm, the oil flow at the main bearings is not significantly increased by the constant bearing clearance (virtually identical thermal expansion coefficients between steel/crankcase and nodular cast iron/bearing shells).
Cylinder Sleeve:
To reduce the wear along the cylinder sleeves to a minimum, a production method was chosen whereby a highly porous sleeve (25% silicon and 75% air) is cast directly into the crankcase.
When the sleeve is cast, the air escapes and the silicon remains locally along its path (hence the name LOKASIL).
Bearing Case With Oil-Spray Nozzle:
The Boxster's engine has oil-spray nozzle, used for cylinder cooling to reduce the piston temperature. The injection nozzles are inserted in the bearing case (arrow). To ensure that the engine oil pressure is retained at low engine speeds and at high engine oil temperatures, the nozzle has an opening pressure of 1.8 bar.
Crankshaft:
The drop-forged crankshaft has seven bearings and has 12 counter weights. The main bearing 4 is a thrust bearing. The axial clearance is determined by two stop disks which are inserted into the bearing case halves of cylinder line 4 - 6.
Connecting Rods:
The forged connecting rods are broken apart at the large connecting-rod eye after processing.
Due to the breaking pattern, the two parts are centered in relation to each other Since each breaking pattern has a different shape, no pairing number is necessary.
Belt Pulley:
Marks can be found on the belt pulley and the crankcase to facilitate maintenance and repair work.
Pistons:
Image Legend:
1 Rectangular ring, nitrided steel, 1.2 mm symmetrically crowned.
2 Taper face ring, gray cast iron, 1.5 mm.
3 Three-part oil ring, nitrided steel, 2.0 mm.
The cast aluminium pistons are covered with an iron coating serving as the sliding layer. The piston-pin hole is offset by 0.8 mm towards the intake side.
Cylinder Head:
Cylinder Head - Cross Section View:
The cylinders of the Boxster also have a range of special construction features, e.g. four-valve technology, camshaft adjustment, and hydraulic valve clearance compensation which helps to reduce necessary maintenance.
The four-valve technology improves cylinder filling. The implementation of liquid cooling in this engine which can compensate the increased thermal load placed on the engine resulting from the multi-valve concept allows four valves per combustion chamber to be used.
Three-Part Cylinder Head:
The cylinder head construction comprises the actual cylinder head, the camshaft housing, and the cylinder-head cover. Since the cylinder head comprises three parts, all of the oil channels can be formed in the casting pro cess which means that virtually no holes have to be drilled. Cleaning processes during production are no longer necessary and process safety is increased. The materials and production processes for the individual components are selected to suit the specific application. As a result, parts used for flat-base tappet bearings have a more wear-resistant material composition than those which take the valve seats. A distinction is therefore made according to the specific function and material.
VarioCam:
VarioCam, the adjustment of the intake camshafts, produces a major part of the engine output, the engine torque as well as the good exhaust values at idling speed in the case of engine speeds of 1,200 rpm and 5,120 rpm.
Engine speeds below 1,200 rpm produce a slight overlap in the valve stroke curves for the intake valves in relation to the exhaust valves.
This particularly affects low proportions of hydrocarbons (HC proportions) in the exhaust gas before the catalytic converters. If the engine exceeds the 1,200 rpm mark*, the intake camshafts are adjusted by 12.5 (by 25 if measured at the crankshaft).
Adjustment of the camshafts is such that a greater overlapping of the valve stroke curves for the intake and exhaust valves is produced. This results in improved cylinder filling and thus an increase in engine torque. In the case of engine speeds above 5,120 rpm, the intake camshafts are returned to the basic control times (as for engine idling speed).
If the intake valve closes later, additional amounts of intake air can be drawn in. This produces a recharging effect since the flow of air is not interrupted. This also results in improved filling of the cylinders and an increase in performance.
*The value 1,200 rpm increases to 1,480 rpm with engine oil temperatures of approx. 130°C and above.
Chaingear:
Image Legend:
1 Chain tensioner
2 Tensioning rail
3 Sliding rail
4 Drive wheel, crankshaft (24 teeth)
5 Drive wheel, intermediate shaft (36 teeth)
6 Output wheel, intermediate shaft (21 teeth)
7 Drive wheel, exhaust camshaft (28 teeth)
8 Output wheel, exhaust camshaft (21 teeth)
9 Drive wheel, intake camshaft (21 teeth)
10 Duplex, roller chain
11 Duplex, roller chain
12 Simplex, roller chain
13 Flat-base tapper
14 Intake valve
15 Exhaust valve
Intermediate Shaft:
The intermediate shaft is driven by the crankshaft via a duplex roller chain with a transmission ratio of 0.67 : 1 (24 teeth on the crankshaft and 36 teeth on the intermediate shaft).
Camshaft:
The exhaust camshaft is driven by the intermediate shaft via a duplex roller chain with a transmission ratio of 0.75 :1(21 teeth on the intermediate shaft and 28 teeth on the camshaft) so that the overall transmission ratio of 0.5 :1 is produced for the crankshaft relative to the camshaft.
The intake camshaft is driven by the exhaust camshaft via a simplex roller chain with a transmission ratio of 1:1.
All four camshafts are hollow-cast from high-quality hardchilled steel.
Valves, Valve Springs:
The exhaust and intake valves have a shaft diameter of 6 mm.
The valve springs are single conical springs.
Oil Circulation:
Image Legend:
1 Oil sump
2 Oil suction snorkel
3 Oil pump
4 Overpressure valve
5 Full-flow oil filter
6 Intermediate shaft
7 Oil-to-water heat exchanger
8 Camshafts
9 Crankshaft
10 Oil return pumps
11 Chain tensioner
12 Oil pressure sensor
13 Valves for piston cooling
14 Oil-level sensor
15 Hydraulic valve tappet
16 Oil temperature sensor
Oil Supply:
In order to ensure a reliable engine oil supply even with extreme longitudinal and lateral acceleration, the Boxster has an integrated dry-sump lubrication system (without external oil tank), i.e. the oil sump is situated opposite the crankgear.
A special die-cast method means that it is possible to cast the oil channels into the crankcase. As a result, drilling as well as the subsequent cleaning processes are no longer necessary.
The oil pump (3) driven via the intermediate shaft (6) draws the oil out of the oil sump (1) via the oil suction tube (2) and then transfers it to the lubricating points.
Oil Repeller:
The oil repeller leads the returning oil back to the oil sump via the oil collection channel and collection edge.
Oil Return Pump:
Since there is no drop between the cylinder heads and oil sump in a Boxer engine, the oil is drawn out of each of the cylinder heads by a oil return pump.
Oil Separator:
The oil drawn off via the return pumps is fed into "swirl- pots."
In these containers, the oil is centrifuged and defoamed, i.e. gases which the oil has picked up on the way to the lubricating points are removed.
This ensures that the oil always has a good consistency which is necessary to guarantee the reliability of the hydraulic valve clearance compensation. Gases could bring about changes in the engine timing which would have an effect on the performance and exhaust-emission behavior of the engine.
Oil Filter:
An exchangeable filter cartridge is used as the oil filter.
The oil capacity is 8.25 liters.
The engine oil must be changed every 15.000 miles, the filter cartridge must be changed every 30.000 miles.
Oil-Level Sensor:
Information regarding the oil level displayed on the instrument cluster is provided via a measuring sensor screwed into the crankcase.
Cooling System:
Image Legend:
1 - Water pump
2 - Crankcase
3 - Thermostat
4 - Radiator
5 - Heat exchanger, heating
6 - Oil-to-water heat exchanger
7 - ATF heat exchanger (Tiptronic only)
8 - Electric shut-off valve (Tiptronic only)
9 - Expansion tank
10 - Shut-off valve
11 - Venting line (engine)
12 - Venting line (radiator
The principle of cross-flow cooling with integrated cooling-water channelling was implemented to ensure that the cooling water is distributed evenly to all of the cylinders. A temperature drop between the individual cylinders is thus prevented. The cooling fluid is supplied through integrated lines.
As already described in the casting techniques under Oil circulation, all of the cooling channels in the engine are produced in the casting process. Additional lines or hoses in the engine are no longer required which, in turn, results in high reliability and low servicing requirements.
Service Tray:
In the luggage compartment (bottom right), there are the filling spouts for the cooling fluid (right, blue cap) with expansion tank as well as for the engine oil (left, yellow cap) and the oil dipstick.