At this year’s Detroit auto show, Ford’s F-150 nabbed headlines with its courageous move from steel to aluminum for the entire cab and bed, potentially saving hundreds of pounds. Equally courageous, but less reported, is Ford’s choice of ma­teri­als for the 2015 F-150’s 2.7-liter twin-turbocharged “Nano” V-6 engine: It has a cast-iron cylinder block. Conventional wisdom says that iron is too heavy for modern cars and trucks. Ford’s first manufacturing genius, Charles “Cast-Iron Charlie” Sorensen, earned his nickname by integrating the Model T’s major engine and transmission components into just a few castings.

But during the past two decades, engineers have systematically switched blocks and heads from iron to aluminum to save weight. So why the seemingly retrograde move to an iron block for the F-150’s 2.7-liter V-6, especially when this truck’s three optional engines all have aluminum blocks and heads? Because iron makes the most sense from an engineering perspective, and the most cents for the Ford Motor Company. In the 1950s, metallurgists began developing cast iron vastly superior to the Model T stuff. All cast iron is a mix of iron and graphite (carbon) with smidgens of other elements to fine-tune its physical properties. Basic gray iron is great for frying pans. Stronger malleable iron makes excellent crankshafts. Nodular iron has higher tensile strength and hardness, ideal for gears and camshafts. 

The best stuff is compacted graphite iron (CGI), which falls between gray and nodular iron in strength and stiffness while providing greater resistance to fatigue cracks.