Nissan has announced that its Decherd, Tennessee, assembly plant will start using a fascinating cylinder-coating technology in the Altima's 2.5-liter, four-cylinder engine, a technology that the company points out has been used in the high-performance GT-R. This isn't the first application of what Nissan calls its "mirror-bore" technology; it has used the coating process in a number of vehicles. But it's worth taking a minute to examine the interesting advantages being implemented in the Altima's PR25DD engine.
Most engines that feature an aluminum block use a pressed-in iron cylinder liner for durability. Aluminum simply isn't very tough, and a piston (and its steel rings) moving around in an uncoated aluminum cylinder bore would destroy it fairly quickly. Iron is much more durable, yet still much lighter than an entirely iron engine block.