If you’ve ever come across a conversation on a web car forum — especially those geared towards imports — or listened to someone wax enthusiastic about the newest WRX, EVO, or Audi, you’ve probably heard a lot of all-wheel drive (AWD) terms and explanations thrown around, not all of them accurate. Everybody seems to be using terms like torque split and viscous coupling. Planetary center differentials, Quattro, and limited-slip differentials (LSDs) pop up often. What is a Torsen anyhow? I hope to set the record straight and clarify what really goes on inside of all-wheel drive systems. This article will cover passive systems found commonly through the 1990s and into the present, to be supplemented later by an article on more sophisticated active and electronically-controlled systems that have come into high-end use.

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I have seen many people talk about OBD-II emissions tests on various web forums.  Often with a puzzled: “I failed readiness!” or “Do I have to do an OBD-II test on my 1994 vehicle?” Since OBD-II has replaced or will replace sniffer tests for 96 and newer vehicles in most states, I thought I’d dump some introductory information about OBD-II emissions tests for people.  I don’t get into the details about OBD-II, the various protocols, or how to tune an OBD-II vehicle here.  Only what to expect in the emissions process.

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