The vast majority of the pressure drop and flow restriction is the filter housing, not the filter.

Part of this is for sound reduction -- diesel intakes are pretty noisy with no throttle valve in there to contain the noise of the air getting sucked through the engine.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!