Engine - S38 Description and Specifications
87BMW09GROUP 11 Engine
Bulletin Number 11 03 86 (2053) Page 1 of 7
Montvale, NJ February 1987 Technical Dept.
SUBJECT: Six-cylinder, 24-valve engine (S38)
A high performance 24-valve engine (based on the 3.5 liter engine block) has been developed by Motorsport GmbH for the 5- and 6-Series M-models. This engine (S38) is, basically, the same engine (M88) used in the famous M1 model. With a displacement of 3.5 liters and a catalytic converter, the S38 engine develops 256 hp (SAE net) at 6500 rpm.
Although this engine was primarily designed for high performance, additional design objectives were incorporated to make it more suitable for every day use. These objectives are low noise level, good response at part load, smoothness over a wide engine speed range and ease of maintenance.
The high power output is achieved mainly by use of a two-deck, crossflow aluminum cylinder head with 4 valves per cylinder (2 intake/2 exhaust valves) and twin overhead camshafts, running in seven bearings each. The camshaft bearings are split, allowing the camshafts to be removed upward.
To ensure reliable sealing, the cylinder head gasket has edges of stainless steel around the combustion chambers/cylinder bores.
The 4 valves are arranged in a V-configuration, with the exhaust valves operated by one camshaft and the intake valves by the other. Four valves per cylinder increase volumetric efficiency and allow quicker gas flow through the engine. As the weight of the individual valves is lower compared to the usual 2-valve engine, they can be opened and closed more rapidly by using steeper flanks on the camshaft lobes.
The valves are operated directly by the camshafts and bucket-type tappets (2). Valve clearance is adjusted by shims (1) located in the bucket tappet (2) without removing the camshafts. Double valve springs ensure positive valve opening and closing at high engine speeds.
A double roller chain is used to drive the camshaft. A hydraulic chain tensioner maintains constant tension and a low noise level in all speed ranges. The combustion chambers are in the cylinder head and include a squish area. This ensures good turbulences of the air/fuel mixture around the centrally located spark plug. This configuration with its short flame path allows a compression ratio of 9.8:1.
Piston weight has been reduced to enhance mechanical efficiency and minimize friction. The piston pin was moved closer to the piston head by using a 9 mm longer connecting rod. To prevent any possibility of the valves hitting the piston, four pockets are provided in the piston head.
Most of the engine block components, such as the block itself, oil pan, oil pump, flywheel, water pump, alternator, crankshaft and crankshaft bearings are the same as for the 2-valve 3.5 liter engine before the E32 modifications.
The vibration damper mounted on the front end of the crankshaft had to be modified due to the specific requirements of this engine. For optimum engine cooling, the coolant flows out of the cylinder head to the thermostat housing via a large aluminum pipe on the exhaust side of the cylinder head.
The standard oil filter head is used for control of the oil circuit including the oil cooler in the front spoiler.
A new 5-speed manual transmission (see Technical Reference Information 23 01 86 (2050)) has been developed for the S38 engine. The contact pressure of the (240 mm diameter) clutch pressure plate has been increased to 8000 N to transmit the high engine torque.
Fuel injection and ignition of the S38-engine are regulated by the well known MOTRONIC system (without adaptive control). An engine speed and reference sensor are mounted on the flywheel side of the engine. The system features electronic idle control, cold start control and warm-up enrichment. The 30 kV distributor is mounted to the exhaust valve camshaft. Fuel system pressure is 3.0 bar. An atmospheric pressure sensor provides compliance with emission standards at different altitudes.
Intake and exhaust system had to be completely redesigned to achieve optimum gas flow without unnecessary flow restrictions.
Six separate intake funnels connect the one piece intake manifold to the six separate intake pipes. Each intake pipe has its own throttle plate. The throttle plates are operated synchronously in three groups of two via three linkage shafts connected to a central shaft running on needle bearings. The synchronized operation of the throttles assures excellent emission control and fast engine response.
As part of the PDI (as well as with every engine washing), the bearings and the balls and sockets of the entire throttle linkage have to be lubricated with Molykote Long Term Grease, BMW P/N 81 22 9 407 007.
The exhaust gas leaves the engine through a fan-shaped manifold (each cylinder has its own exhaust pipe). Three pipes then go into one collector pipe. These two collector pipes enter the catalytic converter via a crosspipe, where the oxygen sensor is located.
The idle mixture does not have to be checked/adjusted during inspections. However, checking and/or adjusting the idle mixture is still required for troubleshooting or repairs. The basic adjustment procedure is described below. For specific and current values/details always refer to the current Nominal Value and Repair Manual microfiches! For the idle mixture adjustment, the engine must be at operating temperature (oil temperature 60~C), and the air pressure sensor connected.
Idle Adjustment
Pull off throttle switch plug and bridge pins 2 and 18 in the plug to ensure a closed throttle signal to the Motronic Control Unit.
Adjust idle speed by turning the central air control screw (3) to 840 rpm.
Connect pressure gauge to each vacuum tap one after the other, after having removed the corresponding rubber cap (1).
Note all six values, which must be in the range of 300 +/- 50 m bar.
For proper intake vacuum synchronization all single throttle plates have to be adjusted by turning the individual bypass screw (4) within +/- 5 mbar of the average vacuum (add up all 6 values and divide this number by six; this will give you the average vacuum). Install new anti-tamper device (2) and reinstall rubber cap (1) after adjustment.
Then check idle speed again (required 840 +/- 50 rpm) and adjust by turning the central air control screw (3), if necessary.
CO-Adjustment
Connect Service-Tester to exhaust manifold CO-screws.
Measure CO with oxygen sensor connected. If CO is out of specifications (0.8 +/- 0.4%) verify if oxygen sensor is working. Pull off and plug vacuum hose on fuel pressure regulator. Oxygen sensor is okay if it regulates the CO level back to the previously read value after a brief rise.
After having verified the proper function of the oxygen sensor, unplug it. Adjust CO by turning the CO control screw in the air flow meter. Reconnect oxygen sensor, check idle and CO, and readjust if necessary.
Remove jumper wire from throttle switch plug and reconnect plug to throttle switch. Finally check idle and CO and adjust throttle switch, if necessary.
Engine Power (kW) and Torque (N-m) Curves
This engine is to be run with UNLEADED PREMIUM gasoline only (at least 93 AKI).
TECHNICAL DATA