The 6-cylinder engine is quite different from the five. The six cylinders are 'paired,' which allows the use of resonance techniques. You can't do that with five cylinders, which is why the 605 doesn't have flaps. Additionally, with five cylinders, getting reasonable smoothness becomes more important than a few horsepower.

In the factory's 1995 "Intoduction into service" manual, the resonance flaps are described along with a graph showing the difference with and w/o the flaps. I suspect it would require a dyno to show the effect—the text and graph didn't have any numbers attached.

The flaps change state at ~2500 and ~3500 RPM. I have added LEDs to my speedometer so I can see and confirm they are working. The 1996-97 engines in the W210 models also have flaps; I suspect a malfunctioning or disconnected flap in those engines would set a code. The 1995 W124 is spared that foolishness.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970