The 5.4-liter supercharged aluminum V-8 in the '11 Shelby GT500 is 100 pounds lighter than it predecessor. Eight pounds of that comes from an absence of traditional cylinder liners. What do the Nissan GT-R and GT500 have in common? This.
The Nissan GT-R is a technological tour de force, and its wizardry begins at the most basic level: the cylinder liners in its twin-turbocharged aluminum V-6. Simply put, there aren't any. Here's the funny thing, though — the technology that Nissan uses to accomplish this feat was actually developed and patented by Ford.
The process in question is called plasma-transferred wire arc (PTWA). It basically involves blowing a fine mist of molten steel at high speed onto a rough surface and then honing that surface into a perfect cylinder bore. It's something that Matthew Zaluzec, Ford's manager of materials and nanotechnology, has been working on since 1991. As the concept was being refined, Ford brought in partners Flamespray and Honsel to finish the development work. The two firms were also responsible for manufacturing and marketing the twenty-five patents that resulted from the research.
The amazing part about this process is its relative simplicity: Spray-on surface processes have been used in aerospace applications for two decades, but until recently, the costs that work in that environment haven't been compatible with mass-market products. It starts with the engine block — aluminum in this case — where the surface to be coated is roughed up in order to give the liner material something to adhere to. Next, specially designed equipment uses an argon-hydrogen plasma arc to atomize an advancing 1010 steel alloy 1/16th-inch wire (basically welding wire). The atomized wire is then sprayed against the cylinder wall at 358 mph. The head lays down layer after layer of this material. Because the particles are so small, they splatter and transfer heat rapidly. They leave behind layers of iron and a ferrous oxide called Weustite (no, it's not rust); these layers build up to a thickness of roughly 0.6 mm, and the block is then honed to a cross-hatch pattern and given a final liner thickness of roughly 150 microns.
Check out Honsel's video of the process below:
When we think of engines without pressed-in cylinder liners, our thoughts turn to the disastrous Jaguar Nikasil engines in X308 Jaguar XJRs. (Or, for that matter, BMW's early M60 V-8s.) The liners in both cases failed when when exposed to high-sulfur fuels, and they required a massive recall that usually resulted int the entire engine being replaced. Is this process similar? Not at all. Nikasil was a nickel-silicon material electroplated to engine blocks; this is an iron/iron oxide liner sprayed in at high temperatures. It basically replaces a thick press-in iron liner with another iron liner, albeit one significantly lighter and roughly the thickness of a human hair.
Wondering about durability? We did, too. Ford claims to have taken taken beat-to-hell durability-cycle engines with the equivalent of 250,000 miles of wear and, upon inspection, discovered that the initial hone patterns appeared brand-new — the piston rings hadn't polished them away. That freakishness is due in large part to Weustite's molecular qualities. Its crystalline structure, in conjunction with microporosity created by the layering process, acts as an oil sponge, allowing pistons to slide smoothly while reducing oil consumption.
That, however, isn't the best part. Here's where it goes from "Gee, that's pretty neat" to "no way": Amortized out, this process is actually cheaper than a pressed-in cylinder liner. These machines can line virtually any bore diameter quickly and cheaply, and the process is both fast and easily scaleable. As an added bonus, it's accurate enough that no piston-to-bore matching is required — the factory uses one size of piston, period.
Should you expect to see this in future Ford products? Absolutely. The GT500 was chosen first because it's a good environment for trying new technologies, but spray-in liners are headed for large-scale production. Sadly, there is one downside — all of this wonderful technology will put an end to boring out an engine block for bigger displacement, at least on a grassroots scale. Still, we we think the benefits are worth the sacrifice.