It\u2019s Where You Wind Up That Matters \u2013 Porsche All Wheel Drive\r\n\r\nAs a good New Englander, you probably own a car that is \u201cgood in the winter.\u201d That may mean simply fitting snow tires, driving more carefully in the snow, or adding some mechanical advantage - such as front wheel drive or all wheel drive (or four wheel drive - yes, it\u2019s technically different, I know). Whatever your solution to the problem of slippery surfaces, how much do you think about how your vehicle does what it does?\r\n\r\nPorsche recently introduced their latest Carrera 4 and 4S models with new tech besides the standard 992 changes - a liquid-cooled front differential for the all wheel drive system. As an owner of a 2007 Targa 4 with AWD (not to mention a string of Cayenne\u2019s), I was curious why they would bother investing time in a system that most of us won\u2019t ever really think about. Liquid cooling implies that the goal is to disperse heat, right? Why is there heat here to worry about? I was curious so I did what anyone does these days and Googled it.\r\n\r\nIf You Can't Take The Heat\r\nAs I\u2019m sure you know, when a car turns, the wheels on one side go faster than on the other. This is because the wheels on each side are suddenly following two different arcs with two different radii. All that high school geometry is coming back to you, right? But why clear those cobwebs? Well, if you solidly connect all those wheels together, they get themselves into a literal bind. That binding pressure builds up and has to go somewhere. The mechanical bits - drive shafts, gears, etc - have to absorb these differences in rotational speed somehow. To get out of this bind (known as torque-wind), the parts might break or they might deflect and bend. This, of course, ends badly. We need to add something with a bit more give in this situation - a \u201cdifferential\u201d - a brilliant little bit of engineering that allows a wheel on one side to temporarily \u201cslip\u201d a bit and go a different speed. The price you pay for this controlled slippage without breaking? Usually that energy from the \u201cslip\u201d is dissipated as heat, often through a clutch pack or viscous coupling device of some sort. There is always a price to pay.\r\n\r\nDuring my 4am Googling, I came across a cool article from Design News in 1995. It recounted the history of how Borg-Warner (the transmission folks) came to develop the 1995 \u201cControl Trac\u201d system for Ford\u2019s Explorer, etc.\r\n\r\n\r\nThe many options of Control Trac AWD in a Ford (Copyright Four Wheeler magazine)\r\n\r\nIt was a great story arc that went from an origin of concerns about the fuel economy of four-wheel-drive systems born in the 1970\u2019s and how saving every drop of fuel became a primary design goal - sound familiar? The Borg Warner chaps decided that being able to disengage a four wheel drive system\u2019s front wheels manually at the hubs just would not do. Would you want to have to hop out in the snow and mess with turning some big dials on the front of your car? How plebeian. Our computer overlords could surely do a better job of doing this for us.\r\n\r\nIn the 1980\u2019s they set to work fitting a dodgy station wagon with a prototyped computer-controlled torque sensing/splitting central transfer case that did away with the center differential completely - by using sensors to react to wheel spin by sending more torque to the front wheels via an electronically-controlled clutch (clutches are basically two spinning discs that rub together to different degrees to vary the rotational speed differences between them - but they get hot with all that friction). The computer to control the new transfer device took up the whole back seat.\r\n\r\nEventually they found that constant measurements of the change in RPM between various bits told them what they needed to know about slip to tell the central clutch pack to engage and grab some power for the front wheels. They packaged it up and sold it to Ford. As a side note - the clutch material was paper-based - odd choice for a heat-dependent system, no? But they tested it and raced it and it worked - after they made it bigger.\r\n\r\nPorsche's Brand Of AWD\r\nAbout the same time Borg was getting Ford on board, Porsche was putting an all-wheel-drive system into their 959. Interesting case study in economics right there. Porsche\u2019s system was similar, though, in that it used lots of computer-controlled sensors and a computer-controlled clutch pack to go from a pretty even front/rear torque split to as much as 20/80. As far ahead as Porsche was in some ways, the 911 had to make due with a passive viscous-coupling system for all wheel drive up until the computer-controlled clutch pack system went into the 911 Turbo in 2006. The fancy computers didn\u2019t go into the base Carrera 4 until 997 gen 2 in 2008, after the Cayenne helped push the technology along a bit.\r\n\r\nSide note - Porsche\u2019s first all wheel drive car was actually the Type 350 in 1947. Had a flat 12, that one. A Turbo Cabriolet was shown with AWD in 1981. The 935 race car that won the Paris-Dakar came in 1984 leading to the 959 in 1985. And the first 964 C4 came in 1988. For more history: https://presskit.porsche.de/specials/en/30-years-awd-in-porsche-911/topic/highlights.html\r\n\r\n\r\nThe new 992 AWD system\r\nMore Power, Captain!\r\nOnce the technology was in place, what has changed since is...power! (In Jeremy Clarkson voice, of course) The latest base 992 is up to 379bhp and 331lb-ft of torque. My 2007 only had 325bhp and about 270lb-ft. These new turbo base cars are really bringing the torques! I\u2019m betting that this new power, along with ever better and grippier tires, is the reason Porsche is adding some extra cooling to the package. More power means more slip means more heat.\r\n\r\nSo where did we wind up? All that torque wind-up wound up getting me all wound up. And all this so you won\u2019t wind up in a ditch. It truly is all about where you wind up.