Engine Internals: How Does An Engine Work Full Guide

Embark on a journey into the heart of modern machinery—the combustion engine internals.

Discover its varied types, intricate components, precise timing, and the interplay of power and efficiency. From the rhythmic strokes to the symphony of materials, delve into the mechanics driving our vehicles and industries, shaping the world of motion and power.

engine internals

What is an internal combustion engine?

An internal combustion engine is the power source behind many modern machines.

It works by igniting fuel to create controlled explosions, generating energy that powers vehicles, machinery, and devices. Unlike external combustion engines, which use external heat sources to produce steam for power, internal combustion engines create power directly from burning fuel within sealed chambers.

This process converts chemical energy into mechanical work, making these engines vital for cars, trucks, airplanes, and more.

What are the Different Types of Internal Combustion Engines?

Internal combustion engines come in a fascinating array of forms, tailored for specific tasks and functions. Let’s dive into the world of these engines to uncover their diverse types and the unique characteristics that set them apart.

Fuel Types in Internal Combustion Engines

The fuel that an internal combustion engine uses can vary from engine to engine. A good air to fuel ratio for the fuel type will determines how the engine runs and its impact on the environment. Here are the two primary fuel types:

Gasoline: This is the most common fuel for cars and small vehicles. Gasoline engines are known for their smooth operation and ability to deliver a good balance between power and fuel efficiency.

Diesel: Diesel fuel is often used in trucks, buses, and heavy-duty machinery. Diesel engines are known for their impressive torque, which is essential for hauling heavy loads, and they tend to be more fuel-efficient than gasoline engines.

Engine Configuration and Design: Shapes and Functions

The way an internal combustion engine is set up can significantly impact its performance and function. Let’s delve into the main engine configurations:

V-Shaped Engines: These engines arrange their cylinders in two banks, resembling a V shape when viewed from the front. V-shaped engines often strike a balance between power and space efficiency, making them popular choices for a wide range of vehicles, from cars to trucks.

Inline Engines: In this configuration, cylinders are aligned in a single row. This straightforward design simplifies manufacturing and maintenance, and it’s frequently used in smaller vehicles where space optimization is key.

Flat/Boxer Engines: Cylinders are horizontally opposed in flat or boxer engines, resulting in a low center of gravity and smoother vibrations. These engines are commonly found in some sports cars and aircraft.

W-Shaped Engines: This configuration features three banks of cylinders forming a W shape. It’s often used in high-performance vehicles where space constraints require compact yet powerful engines.

H Engines: H engines have two sets of cylinders positioned in a V configuration but sharing a common crankshaft. This layout is used in some luxury cars and high-performance vehicles.

Opposed Piston Engines: In this design, two pistons move in opposite directions within a single cylinder. It’s known for high power density and fuel efficiency and finds use in certain military and industrial applications.

Rotary Engines: Also known as Wankel engines, these have a unique rotary design with triangular rotors instead of pistons. They offer high power-to-weight ratios and were used in some sports cars.

Each configuration brings its own set of advantages and considerations, shaping the engine’s characteristics and best-suited applications. Understanding these layouts provides insights into the versatility and adaptability of internal combustion engines across diverse industries.

What is Engine Displacement?

Engine displacement measures the space inside an engine’s cylinders where combustion occurs. It’s like the engine’s breathing room for creating power. This measurement, often in cubic centimeters or liters, directly affects how much power the engine can generate and its efficiency.

Simply put, larger displacement means more air and fuel can be used to make power. But it’s not just about size – cylinder design and arrangement matter too.

Engines vary in displacement, like 2.0-liter or 3.5-liter. These numbers show the total cylinder volume. Bigger engines suit power-hungry needs like trucks; smaller ones prioritize efficiency in compact cars.

Engine displacement is a core factor affecting performance. It influences power, torque, fuel efficiency, and overall usability.

The main Engine Internals Breakdown

Engines are made from hundreds of pieces all working together to create power and move your car. To help you further understand how engine works here is a list of the primary engine internals:

Engine internals 1: The block

Imagine the cylinder block as an engine’s core. It houses the cylinders where combustion occurs. Everything is intricately linked here, ensuring the engine runs smoothly and generates power accurately. In essence, the cylinder block is the engine’s foundation, uniting cylinders and parts to bring your engine to life.

Engine internals 2: The Cylinder head

Think of the cylinder head as an engine’s command center. It sits atop the cylinder block like a cap, sealing the cylinders and hosting essential components.

This vital part houses the valvetrain that controls air and fuel flow in and out of the cylinders. The spark plugs, also find their home here, igniting the air-fuel mixture to start the power party.

In essence, the cylinder head orchestrates the combustion process, allowing air, fuel, and spark to come together in a controlled dance for power generation.

Engine internals 3: The pistons

The pistons slide up and down inside the cylinders, converting the energy from fuel combustion into mechanical force.

When the spark ignites the air-fuel mixture, it creates a controlled explosion. This explosion pushes the piston downward, turning the crankshaft and generating power. Once that energy is used, the piston bounces back up to repeat the process.

In essence, pistons are the engine’s dynamic force creators, transforming fiery explosions into the energy that propels your vehicle.

Engine internals 4: The Connecting Rods

Very simply the connecting rod connects the piston to the crankshaft. They play the critical part of converting the up-and-down motion of the pistons into the rotational movement of the crankshaft.

Engine internals 5: The crankshaft

The crankshaft resembles a long, twisting rod with offset crankpins. As pistons move down, the connecting rods push against these crankpins, causing the crankshaft to rotate. This rotation is what transfers the piston’s energy into a spinning motion, creating the power necessary to spin your wheels.

Engine internals 6: The camshaft

Think of the camshaft as an engine’s choreographer, directing the opening and closing of valves that let air and fuel in and exhaust out.This elongated shaft has lobes – like raised bumps – that push against the valves.

As the camshaft rotates, these lobes cause the valves to open and close at precise moments. This timing determines when air-fuel mixture enters and when exhaust exits, optimizing power and efficiency.

Camshafts are synchronized with the crankshaft’s rotation, ensuring the valves move in harmony with piston motion.

Engine internals 7: The valvetrain

Imagine the valvetrain as an engine’s gatekeepers, controlling the flow of air and fuel into the cylinders and the expulsion of exhaust gases. They ensure everything operates in perfect rhythm.

The valvetrain consists of the camshaft, cam followers (or lifters), pushrods (in some designs), and valves. As the camshaft turns, its lobes lift the cam followers, which in turn push open the valves. This precise movement lets air and fuel in for combustion and releases exhaust gases after.

Engine internals 8: the Timing System

The timing system, often using a belt or chain, links the crankshaft and the camshaft. As the crankshaft turns, it drives the camshaft’s rotation. This coordination is crucial because it dictates when valves open and close in relation to piston movement, optimizing combustion efficiency.

The belt or chain is crafted from durable materials, designed to withstand high temperatures and forces. It’s a behind-the-scenes hero, making sure the engine’s intricate movements align seamlessly.

The intake manifold

The intake manifold is a series of tubes or passages that direct air into the cylinders. This air combines with fuel to create the explosive mixture that powers the engine. It’s a crucial part of the combustion process.

If your are interested in knowing more about the intake manifolds check out our full intake manifold guide HERE

The exhaust manifold

The exhaust manifold is a set of pipes that gather exhaust gases from each cylinder and funnel them out through a single outlet. These gases are the byproduct of combustion and need a clear path out of the engine.

Just like intake manifolds, the design of exhaust manifolds affects performance. Smooth, unrestricted flow allows for efficient expulsion of gases, which can improve power generation and fuel efficiency.

Engineering is crucial here, ensuring the manifold withstands high temperatures and pressures while minimizing backpressure.

Fuel delivery system

Imagine the fuel injection or carburetor system as the engine’s gourmet chef, preparing the perfect mix of air and fuel for combustion.

In modern engines, fuel injection is the star. It precisely sprays fuel into the cylinders alongside air for combustion. This precise control optimizes power and efficiency, and it’s managed by the engine’s computer.

In older designs, carburetors took the lead. They mixed fuel and air before sending it to the cylinders. Carburetors were like the engine’s flavor blender, creating the right recipe for power.

Both systems have their merits, but fuel injection is more efficient and adaptable to varying conditions.

Ignition system

The ignition system’s star player is the spark plug. When the air-fuel mixture is compressed in the cylinder, the spark plug generates an electric spark. This spark ignites the mixture, creating controlled explosions that propel the engine.

Four stroke vs two stroke engines

Once again engines come many in different styles. Four-stroke and two-stroke is two of them. When one of these words is applied to an engine, it refers to how many strokes the piston requires to complete a full combustion cycle. Such as the following:

  • Intake
  • Compression
  • Combustion
  • Exhaust

Let’s dive into the distinctions between these two engine designs.

Four stroke Engines

In a four stroke engine each stroke has only one single function. Therefore it follows the list showcased above or the one below.

  1. Intake Stroke: The engine draws in a mixture of air and fuel as the piston moves down. This creates a combustible mix within the cylinder.
  2. Compression Stroke: The piston moves back up, compressing the air-fuel mixture. This compression readies the mixture for combustion, making it highly volatile.
  3. Combustion Stroke: The spark plug ignites the compressed mixture, creating a controlled explosion. This explosion drives the piston down with force, turning the crankshaft and generating power.
  4. Exhaust Stroke: As the piston rises again, it pushes out the spent gases from the previous combustion cycle through the exhaust valve.

Four-stroke engines are known for their efficiency and smoother power delivery. They’re widely used in cars, trucks, and most modern vehicles. Their design allows for better control of combustion and emissions, making them an integral part of the automotive landscape.

Two Stroke engines

Two stroke engines are a bit more complicated to understand. However, the main principle is they achieve the four tasks required in only two strokes.

Furthermore, traditional two stroke engines do not have valves like a four stroke, but rather ports precisely cut in the cylinder wall.

Here’s how they work:

  1. Compression/Combustion: In a single motion, the piston moves up and compresses the air-fuel mixture in the cylinder. At the same time, the spark plug ignites the mixture, creating a quick and intense explosion. This explosion pushes the piston down, turning the crankshaft and generating power. As the piston descends, it also uncovers the exhaust port, allowing spent gases to escape.
  2. Exhaust/Intake: The piston’s upward motion covers the exhaust port, sealing it off. Simultaneously, it uncovers the intake port, allowing a fresh mixture of air and fuel to rush in. This new mixture fills the cylinder, ready for the next compression and combustion cycle.

Two-stroke engines are known for their simplicity and lightweight design. They’re often used in applications where high power-to-weight ratios are crucial, like motorcycles, small power tools, and some recreational vehicles. However, due to the design, they can be less fuel-efficient and emit more emissions compared to four-stroke engines.

The different to of material use for engine internals

Different parts of the engine require specific materials to ensure durability, heat resistance, and performance. These materials will vary from part to part but there is common ones that appear frequently.

Let’s explore the common materials used in engines and how they contribute to the heart of your vehicle’s power.

  1. Cast Iron: Cast iron engine internals are durable and can withstand high temperatures, making them suitable for heavy-duty and high-performance engines. However, they are heavier and may not offer the same efficiency as other materials.
  2. Aluminum: Aluminum engine internals are lightweight, which helps reduce reciprocating mass and improve engine efficiency. They also dissipate heat more effectively. However, they may not be as durable as cast iron in extreme conditions.
  3. Forged Aluminum: Forged aluminum engine internals are stronger and more durable than cast aluminum ones. They are often used in high-performance engines where strength and reliability are crucial.
  4. Steel: Steel engine internals are rarely used in passenger cars due to their weight, but they find application in heavy-duty engines and some specialized racing applications. They offer high strength but may require more complex manufacturing processes.
  5. Cylinder Liners: Some engine blocks, regardless of their primary material, use replaceable cylinder liners made from materials like iron or steel. These liners offer wear resistance and can be replaced without replacing the entire block.

What is a compression ratio?

Engine compression ratio is a fundamental parameter in internal combustion engines that describes the ratio of the cylinder’s volume when the piston is at its bottom-most position (bottom dead center, or BDC) to the volume when the piston is at its top-most position (top dead center, or TDC). In simpler terms, it’s the ratio of the cylinder’s largest to smallest volume.

Mathematically, the compression ratio (CR) is calculated using the following formula:

CR= Volume Max / Volume Min

  • Volume Max:​ is the volume of the cylinder at TDC (top dead center), which is when the piston is at its highest point.
  • Volume Min:​ is the volume of the cylinder at BDC (bottom dead center), which is when the piston is at its lowest point.

The compression ratio has a significant impact on an engine’s performance, efficiency, and power output. Here’s how it influences these factors:

  1. Efficiency: A higher compression ratio generally leads to better thermal efficiency. This is because a higher ratio allows for better utilization of the fuel’s energy, resulting in more work extracted from each combustion cycle.
  2. Power Output: An engine with a higher compression ratio can produce more power, all else being equal. This is due to the increased expansion of the combustion gases, resulting in greater force applied to the piston during the power stroke.
  3. Octane Requirements: Higher compression ratios require fuels with higher octane ratings to prevent knocking.
  4. Emissions: Engine design with specific compression ratios can influence exhaust emissions. A well-designed engine can use a higher compression ratio to achieve better combustion and lower emissions.

Compression ratios can vary significantly between different types of engines and their intended purposes. For example, high-performance engines might have compression ratios above 10:1, while some more conventional engines might have ratios around 9:1 or lower.

What is engine timing?

Engine timing is the precise coordination of valve openings, closings, and ignition events in an internal combustion engine. It ensures that the intake and exhaust valves open and close at the right moments, allowing air-fuel mixture intake and exhaust gas expulsion to occur efficiently.

Additionally, ignition timing ensures the spark plug ignites the mixture at the ideal time for optimal power and efficiency.

Proper timing guarantees smooth engine operation, maximizes fuel efficiency, prevents damage by avoiding collisions between valves and pistons, and enhances overall performance and emissions control.

What is engine knocking and detonation

Engine knocking (also known as detonation or pinging) is an undesirable and potentially damaging phenomenon that occurs within internal combustion engines.

It is characterized by the rapid, uncontrolled combustion of the air-fuel mixture in the cylinder, resulting in multiple flame fronts colliding and creating a knocking sound.

This sound is often described as a metallic “ping” or “knock,” similar to the noise produced when tapping a metal object.

Detonation occurs when the air-fuel mixture in the combustion chamber ignites spontaneously due to high temperatures and pressures, before the spark plug fires. This premature ignition can create pressure waves that collide and create shock waves, leading to the characteristic knocking noise.

Knocking is particularly harmful because it produces sharp pressure spikes that can damage engine components, including pistons, rings, bearings, and valves.

Detonation is problematic for several reasons:

  • Engine Damage
  • Reduced Performance
  • Emissions Increase
  • Fuel Efficiency Drop

Several factors can contribute to engine knocking:

  • Low Octane Fuel
  • High Engine Temperature
  • High Compression Ratios
  • Advanced Ignition Timing
  • Carbon Deposits

Modern engines often incorporate knock sensors and engine control units (ECUs) to detect and respond to knocking. When knock is detected, the ECU can adjust various parameters, such as retarding ignition timing or enriching the air-fuel mixture, to prevent or mitigate the knocking condition.

Overhead Camshaft (OHC) vs. Overhead Valve (OHV)

The terms “Overhead Camshaft” (OHC) and “Overhead Valve” (OHV) are two different types of engine configurations that refer to the placement and operation of the camshaft and valves within an internal combustion engine.

Overhead Camshaft (OHC)

In an OHC engine, the camshaft(s) are located in the cylinder head, above the cylinder(s). The camshaft directly operates the engine’s intake and exhaust valves through mechanisms such as rocker arms, followers, or directly acting on the valves. This design allows for more precise control of valve timing and reduces the overall mass of moving parts within the engine, which can lead to smoother operation and higher engine speeds. OHC engines are often used in modern designs and are associated with more advanced and efficient valvetrain technology.

Overhead Valve (OHV)

In an OHV engine, the camshaft is located within the engine block and operates the valves through a system of pushrods and rocker arms. The valves themselves are located in the cylinder head. This design is also known as a “pushrod” or “valve-in-block” design. OHV engines are older in design and were commonly used in older vehicles, trucks, and larger displacement engines.

In summary, the main difference between OHC and OHV engines lies in the location and method of operating the camshaft and valves.


In conclusion, the internal combustion engine stands as a testament to human ingenuity and innovation. From its humble beginnings to its widespread use in diverse applications, this marvel of engineering has propelled us into a new era of mobility and productivity.

As we continue to refine its design, optimize its performance, and address its environmental impact, we reaffirm the power of human determination to shape the world around us.

With each ignition, each piston’s stroke, and each revolution of the crankshaft, the internal combustion engine reminds us of our ability to transform raw materials into dynamic energy, driving progress and propelling us towards an ever-evolving future.