Benz put a 617 into 300D W115 so there are goodies out there that would make the swap easier. But I think you'd need to use an NA (non turbo) engine, and I think you might need the intake and exhaust manifolds from a W115 300D to get around clearance issues with the body braces that are in the W114/W115 engine bay, intake for sure. The W115 300D air cleaner sits in the RH front corner and is not mounted on top of the manifold like they are in W123 cars. You would also need to supply a vacuum signal for shutting the engine down.

Apart from these issues you'd need a pedal assembly from a stick shift car, or at least the clutch pedal and mounting bar to install into your existing assembly. You'd probably need to have the front section of the driveshaft and shift rods modified to the right lengths. Might look for threads where people have swapped 5 cylinder engines into 4 cylinder W123s to get a sense of all those issues.

If you decide to go for it I've got engine mounting arms and an air filter housing from a W115 300D I'd love to sell, if you need them.

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- Greg -
1973 220D, The Prodigal Benz
1974 240D