I've heard of a lot of OM617 (5 cylinder 3.0L) swaps into offroad machines for their torque and low-end power. A quick search on google pulled up mostly Toyota and Land Rover swaps. Stay away from the 3.5L (350SD), those are the "rod benders" you've heard about. The other ones are all rock-solid for the most part.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth