if you really didnt want a turbo, you could just disconnect the vacuum from the wastegate actuator, and you wouldnt have any boost. dont know why youd want to though. My car ran like this for years without me knowing.

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1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350