What does it mean?
VANOS is a BMW acronym. It refers to the variable valve timing (VVT) system that BMW has incorporated into some of its automobile engine designs. It stands for VAriable NOckenwellen Steuerungi - "variable camshaft control" in German.
So far, engines have been produced with two variants of this system - 'single VANOS' and 'double VANOS.' The modifier refers to how many of the engine's camshafts are equipped with a VANOS system. In the earlier, single VANOS types, only the intake cam was affected by the VANOS system, and adjustments in engine valve timing were made in a finite number of discrete 'steps'. Later, double-VANOS systems however can vary both intake and exhaust valve timing, and are continuously variable to boot.
What does it do?
VANOS is a cam-phasing VVT system. In other words, it operates by introducing a rotational offset to a fixed camshaft in order to change valve timing - it changes the phase of the cam. This is in contrast to cam-changing systems such as the Honda VTEC, which manipulates the camshaft to engage different sets of lobes in order to change timing - and possibly profile as well, or the length of time the valve is open. This allows the engine computer (called DME by BMW, for Digital Motor Electronics) to adjust the timing of the engine as the engine speed changes.
In more general, layman's terms, it provides a serious kick in the pants when goosing a Bimmer hard and reaching around, say, 3200 RPM in a 540i.
Why is this important?
Engine valve timing must be within a certain tolerance range for the engine to function at all. In addition, however, the 'proper' timing of the valves will change as the engine speed changes. For example, as the engine speed rises and the time taken by the piston to cycle shortens, the engine will have less and less time to pull air into the cylinder for each revolution. As a result, as the engine speed rises, the power available from each revolution will drop. However, this can be partially ameliorated by opening the intake valve earlier in the cycle as the speed increases. VANOS allows this. In concert with the ignition timing control provided by an electronic ignition and engine computer, the engine can be 'tuned' in realtime across its RPM range for either more power or better fuel economy.
BMW Engine Types* which incorporate VANOS:
- M50TU: Inline 6 cyl. engine, single VANOS.
- M52: Inline 6 cyl. engine, single VANOS.
- M52TU: inline 6 cyl. engine, double VANOS.
- M54: Inline 6 cyl. engine, double VANOS.
- M62: V-8 cyl. engine, single VANOS after 1998 model year.
- M73: V-12 cyl. engine, single VANOS after 1998 model year.
- S50: Inline 6 cyl. engine, single VANOS.
- S52: Inline 6 cyl. engine, double VANOS.
- S54: inline 6 cyl. engine, double VANOS.
- S62: V-8 cyl. engine, double VANOS.
this is from poking around on various BMW and unofficial enthusiast websites as well as looking at a BMW service CD. This is not
from a single, canonical
BMW source - so verify any data before using it to plan, say, a parts order.
*BMW engines beginning with 'M' are general automotive engines. Engines beginning with 'S' are typically 'Sport' engines - destined for use in the M-series (Motorsport) vehicles such as the M3, M5 and M6. Confusing, no?