If you are sure that no one has swapped engines on the car and that you do, in fact have a 300SD, then it is logical to assume you have a turbo.

You may be able to recognize it on the passenger side of the engine, under the air cleaner. The intake below the air cleaner is in a u-shape- just behind this would be your turbo.

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)