Most engine components are made from cast iron or aluminum alloys, with steel used for the moving parts that endure the highest stress. The specific material chosen for each component depends on a balancing act between weight, heat resistance, strength, and cost. Here’s what goes into the major parts of an engine and why those materials were selected.
The Engine Block
The engine block is the single largest piece of metal in the engine, a solid casting that houses the cylinders, coolant passages, oil channels, and crankcase. Traditionally, blocks have been cast from an iron alloy containing small amounts of nickel and molybdenum for added durability. Iron is rigid, handles high cylinder pressures without flexing, and is relatively cheap to produce. It’s also heavy.
That weight penalty is why aluminum blocks have become increasingly common, especially in passenger cars. An aluminum block weighs roughly half as much as an equivalent iron one, which improves fuel economy and handling. The tradeoff is that aluminum is less rigid. Under extreme loads from turbocharging or nitrous, an aluminum block can twist slightly, potentially causing other components to fail. In practice, though, the difference is shrinking. Modern aluminum block designs have closed the power-handling gap to the point where some engine builders report as little as a 10-horsepower difference compared to iron in high-output applications. Recycled aluminum is also finding its way into engine blocks, since the structural demands are lower than for safety-critical body panels.
Cylinder Heads
The cylinder head sits on top of the block and seals in the combustion chambers. For decades, cylinder heads were cast iron, just like the block. The shift to aluminum happened faster here because the head is where heat management matters most. Aluminum conducts heat about three times faster than cast iron, which helps pull heat away from the combustion chamber and into the cooling system. Air-cooled engines use aluminum heads exclusively for this reason. Today, even many engines with iron blocks run aluminum heads to save weight and improve cooling.
Pistons
Pistons are almost universally made from aluminum alloys, specifically aluminum-silicon blends. The standard piston alloy contains about 12% silicon by weight, along with small amounts of copper, nickel, and magnesium. Silicon is the key ingredient because it reduces how much the piston expands as it heats up. Less thermal expansion means tighter tolerances and less wasted energy.
Some high-performance pistons use “hypereutectic” alloys with 18% or even 24% silicon, which expand even less and resist wear better but sacrifice some overall strength. Beyond the alloy itself, how the piston is made matters. Cast pistons are softer and suited for low-stress engines. Forged pistons, where the aluminum is pressed into shape under enormous force, are denser and stronger. They’re the standard choice in turbocharged, fuel-injected, and diesel engines.
Crankshafts and Connecting Rods
The crankshaft converts the up-and-down motion of the pistons into rotational force. It needs to be extraordinarily strong because it absorbs every firing pulse the engine produces. In everyday engines, crankshafts are cast from iron or steel. For heavy-duty and high-performance applications, they’re forged from 4340 steel alloy, a chromium-nickel-molybdenum blend prized for its toughness. A forged steel crankshaft can handle tensile loads of 140,000 to 150,000 psi, compared to just 65,000 to 100,000 psi for a cast one. After forging, the surface is typically shot-peened to relieve stress, heat-treated for additional strength, and nitrided to resist wear.
Connecting rods link the pistons to the crankshaft. In most engines, they’re forged steel. Smaller engines sometimes use aluminum rods to save weight. The bearing surfaces inside the rod are a different material entirely. The small end, which connects to the piston, gets a bronze bushing. The big end, which wraps around the crankshaft journal, uses precision-fit shell bearings: a steel or bronze backing coated with a thin layer of softer bearing alloy (historically Babbitt metal) that absorbs vibration and protects the crankshaft surface.
Valves and Valvetrain
Engine valves operate in one of the harshest environments in the entire powertrain. Exhaust valves in particular face temperatures that can exceed 1,500°F on every combustion cycle. For most street engines, both intake and exhaust valves are made from a heavy-duty stainless steel alloy called EV8. Stainless steel handles the heat well enough for normal driving and lasts a long time.
When temperatures climb higher, as in turbocharged or supercharged setups, builders turn to nickel-based superalloys. Inconel, a family of nickel-chromium alloys, offers extreme thermal resistance and is a go-to choice for turbocharged race engines and nitromethane applications. Another option, Nimonic 90, is a nickel-chromium-cobalt alloy that can withstand temperatures around 2,000°F without warping.
Titanium valves appear in both racing and some factory performance engines. The Chevrolet LS7, for example, uses titanium intake valves paired with sodium-filled exhaust valves. Titanium is about 30% stronger than steel at nearly half the weight, which lets the valvetrain rev higher without the springs losing control of the valves. Sodium-filled valves use a different trick: the hollow stem is about 60% filled with metallic sodium, which melts at around 206°F and sloshes back and forth as the valve moves, carrying heat away from the combustion chamber and into the stem where it can dissipate.
Gaskets and Seals
Between the block and the head sits the head gasket, which must seal combustion gases, coolant, and oil simultaneously under extreme pressure and temperature swings. Modern head gaskets are multi-layer steel (MLS) designs, consisting of two to five thin sheets of spring steel or carbon steel stacked together. Metal fire rings around each cylinder bore protect against the hottest combustion gases. Older designs used a composite material bonded to a metal carrier sheet, but MLS gaskets have largely replaced them for their superior durability and resistance to blowouts.
High-Performance and Racing Materials
In motorsports, titanium shows up far beyond just the valves. Formula 1 cars use titanium alloys for transmission components, crankcases, turbocharger parts, suspension pieces, and fasteners. MotoGP motorcycles rely on titanium connecting rods, camshafts, valves, and exhaust systems. Even premium road-going sports cars increasingly feature titanium exhaust systems, which save weight and withstand the heat cycling that would corrode cheaper metals over time. Titanium maintains its mechanical integrity up to about 600°C (1,112°F) and resists fatigue from repeated stress cycles, which is why it keeps appearing wherever teams can justify the cost.
Electric Motor Materials
Electric vehicles don’t have combustion engines, but their traction motors are built from a different set of carefully chosen materials. The stator (the stationary part) is wound with copper wire, which carries electrical current to generate a magnetic field. The rotor (the spinning part) in most modern EVs contains permanent magnets made from neodymium iron boron, a rare-earth magnetic material that produces an exceptionally strong magnetic field for its size. This is what allows EV motors to be so compact while still producing high torque. The Toyota Prius, which popularized hybrid drivetrains in 1997, helped establish rare-earth permanent magnet motors as the industry standard, and battery-electric vehicles like the Nissan Leaf followed the same approach. Some manufacturers are now developing motors that avoid rare-earth magnets entirely, using alternative designs to reduce dependence on a supply chain concentrated in a few countries.