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Old 10-13-2011, 11:08 PM
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bluebee bluebee is offline
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Location: San Jose, California
Join Date: Mar 2008
Posts: 25,236
Mein Auto: 02 BMW 525i M54 auto 130K
Originally Posted by dakarm View Post
found this in my search:
To be exact, the DISA valve does not change the length of the intake system on the six-cylinder engines from the M52TU onwards - its function is to be open at low speeds, so feeding all six intake pipes together.

At mid-range speeds it closes, seperating the front and rear groups of three cylinders from each other. At higher speeds it opens again, joining the cylinder groups together. It therefore acts like a massive balance pipe which can be closed when required.

The effect of this is to give more mid-range torque without interfering with bottpm and top-end torque.
I think that explanation is wrong, based on this explanation:
- m54x5[1].pdf

Originally Posted by rdl
- Pages 42 -44 describe DISA operation
below ~ 4000 RPM closed
above ~ 4000 RPM open
rest position, i.e. when removed - flap open
The resonance system provides increased engine torque at low RPM, as well as additional power at high RPM. Both of these features are obtained by using a resonance flap (in the intake manifold) controlled by the ECM.

During the low to mid range rpm, the resonance flap is closed. This produces a long/single intake tube for velocity, which increases engine torque.

During mid range to high rpm, the resonance flap is open. This allows the intake air to pull through both resonance tubes, providing the air volume necessary for additional power at the upper RPM range.

When the flap is closed , this creates another "dynamic" effect. For example, as the intake air is flowing into cylinder #1, the intake valves will close. This creates a "roadblock" for the in rushing air. The air flow will stop and expand back (resonance wave back pulse) with the in rushing air to cylinder #5. The resonance "wave", along with the intake velocity, enhances cylinder filling.

The ECM controls a solenoid valve for resonance flap activation. At speeds below 3750 RPM, the solenoid valve is energized and vacuum supplied from an accumulator closes the resonance flap. This channels the intake air through one resonance tube, but increases the intake velocity.

When the engine speed is greater than 4100 RPM (which varies slightly - temperature influenced), the solenoid is de-energized. The resonance flap is sprung open, allowing flow through both resonance tubes, increasing volume.

Note: With 12 volts DC to the DISA valve, the 'magnetic valve' closes the DISA flap; when you remove the 12 volts DC, the DISA flap flips back open due to spring tension.
- Strange results from a simple test of the M54 DISA valve today

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