Engine - S38 Revised Design: Overview
90bmw04GROUP 11 Engine
Bulletin Number 11 02 96B(2099) Page 1 of 11
Woodcliff Lake, NJ March 1990 Service Engineering
SUBJECT: Six Cylinder, 24-Valve Engine (S38 836) with 3.6 Ltr. Displacement
To power the new M5 (E34), the well-known and proven S38 engine has been revised to achieve even higher power and torque outputs.
At the same time the engine remains well-suited for everyday use, displaying its other virtues of low noise level, good response at part load, smoothness over a wide engine speed range, and last but not least, ease of maintenance.
Even though the maximum power output was raised to 311 hp (SAE net) @ 6,900 RPM, and the max. torque to 265 lb.ft. @ 4,750 RPM, at least 80% of the engine's maximum torque (that is, at least 212 lb.ft.) is available over the speed range between 2,900 RPM and the redline of 7,250 RPM.
The compression ratio was raised to 10.0:1, requiring unleaded premium grade gasoline of at least 90 AKI (95 RON). The higher power output is a result of both greater displacement and careful tuning as well as design changes, improving volumetric efficiency and reducing pumping losses.
This was achieved by increasing the cross section of both induction and exhaust components; an electronically controlled ram air induction system has been developed specifically for this engine.
Basically, it varies the effective length of the induction system depending on engine speed, load and ignition switch position in order to obtain an improved torque spread over a wide speed range.
RESONANCE FLAP CONTROL CIRCUIT DIAGRAM:
In order to improve exhaust emissions, an air injection feature has been added.
Using a belt-driven pump, air is injected into the exhaust manifolds during engine warm-up until the catalytic converter has reached its operating temperature. This is to encourage oxidation of carbon monoxide and hydrocarbons contained in the exhaust gas, converting these compounds into carbon dioxide and water, respectively.
Since both systems, the resonance flap control and the exhaust air injection, utilize vacuum to activate their respective actuators and/or valves, below diagram is used to depict the basic function, component location and interaction of both systems.