A Comprehensive Guide to Auto Engines and Performance
Whether you’ve never had an interest in cars at all or you wanted to learn but never did, we’re all here for one thing: to learn about engines and performance. The engine is a complex and exciting component that has a huge impact on your car’s performance in many different areas.
The engine is your car’s power plant. Without one, your car won’t move. While cars have gone through a lot of changes in the last 130 years, all engines still have the same three basic requirements – air, fuel, and ignition.
This mixture of air and fuel is compressed within a cylinder, making it extremely combustible. The ignition ignites the mixture, creating power. Bigger engines can give your car more power and speed while smaller engines may increase your fuel economy.
Types of Combustion
There are two primary types of engines. The external combustion engine uses the energy made from fuel that burns outside of the engine to power the vehicle. The engine contains fluid that is heated by combustion from an external source. A common example of external combustion engines is a steam engine. These used to be common in locomotives and ships. With the advent of diesel, steam engines were replaced because the energy loss, when compared to diesel, was much greater.
Today, cars use internal combustion engines, which get their power from burning fuel inside the engine. The energy created the fuel and air inside the engine combust moves the pistons and powers the car. Interestingly enough, most people think external combustion came first when in fact, people as early as the sixteenth century built the first internal combustion engines.
History of Internal Combustion
These first internal combustion engines were made using gunpowder as the fuel to move the pistons. The cylinder was stuffed with gunpowder and the gunpowder was ignited underneath the piston. When the gunpowder exploded, it formed a vacuum that would suck the piston down into the cylinder. It was dubbed the atmospheric engine because of its reliance on changes in air pressure. Unfortunately, it wasn’t very efficient, and it was abandoned for steam engines in the seventeenth century.
It wasn’t until 100 years later in 1860 that an internal combustion engine was invented that both worked and was reliable. The engine was patented by Jean Joseph Etienne Lenoir from Belgium. The engine worked by injecting natural gas into the cylinder. The gas was ignited by a permanent flame close to the cylinder. This process is similar to the atmospheric engine, but the flame is permanent, so it was slightly more efficient.
In 1864, Eugen Langen and Nicolaus August Otto started a company making engines like the one Lenoir invented. Eventually, Otto left the company to work on his own engine design that he had been experimenting with since 1861. This design was the beginning of what is now the four-stroke engine and this basic design is still used in cars today.
Car Engine Anatomy
Car engines can be quite complicated. There are a lot of moving pieces and until you completely understand the terminology. Small engines, like those found in lawnmowers, contain only one cylinder and one piston but operate using the same principle. While cars have multiple cylinders to produce more power, you can apply the same idea. If we look at the main components of your engine as well as how one cylinder works, you can better understand how everything works together.
Your engine block is the main component of your engine. It is typically cast from aluminum alloy or iron, but the aluminum alloy is used more often. It’s also called a cylinder block because there are big tubes cast into the structure called cylinders. These cylinders are where the pistons move up and down.
The more cylinders you have, the more powerful your engine will be. There are also other passageways and ducts built into your engine block to allow fuel, oil, coolant, and other needed fluids to flow through the various parts.
If you’ve ever wondered why an engine might be called a V6 or a V8, here’s your chance to find out. The letter refers to the shape of the cylinders while the number refers to how many cylinders it has. Four-cylinder engines have – you guessed it – four cylinders. They’re typically laid out in a straight line above the crankshaft. This format is called an inline engine.
Some four-cylinder engines have two banks of cylinders that are laid horizontally on either side of the crankshaft. This design is called a flat-four.
If your engine has more than four cylinders, they’re typically divided evenly into two banks, although in some cases they can be inline or in a W shape, but those are less common. These two banks of cylinders form a V shape. If you have six cylinders, it’s called a V6, if you have eight cylinders, it’s called a V8, if you have ten cylinders, it’s called a V10, and so on.
This is where all the magic happens. Fuel, air, electricity, and pressure mix to create small explosions that move the pistons up and down, creating power and moving your vehicle forward. The cylinder, piston, and cylinder head make up the combustion chamber. Each cylinder has its own combustion chamber.
The cylinder provides the walls of the chamber while the piston and the cylinder head serve as the floor and ceiling respectively. When fuel and air mix here, they combust, creating thermodynamic energy that powers the pistons.
The piece of metal that sits on top of the cylinders is called the cylinder head. The cylinder head contains small indentations cast into the metal to make room for combustion at the top of each chamber. There is a head gasket to seal the joint between the cylinder head and the engine block. Mounted to the cylinder head are spark plugs, fuel injectors, and outtake valves, which we will define later.
Pistons look like soup cans turned upside down. They move up and down in the cylinder. When combustion takes place in the chamber, the piston moves down, turning the crankshaft. The piston is attached to the crankshaft with a connecting rod or con rod. The piston attaches to the con rod with a piston pin and the con rod connects to the crankshaft with a con rod bearing.
The top of the piston contains three or four grooves in the metal where the piston rings go. These rings are the part of the piston that touch the cylinder as it moves up and down. Piston rings are made of iron. Compression piston rings, of which there are two, are at the top and press out on the walls of the cylinder to create a seal for the combustion chamber.
Oil piston rings, of which there is always one, but sometimes two, are below the compression rings and prevents the oil in the crankcase from leaking into the combustion chamber. It serves to move oil from the walls of the cylinder back into the crankcase where it should be.
As the pistons move up and down, they turn the crankshaft, which converts that up and down motion into a rotation. The crankshaft fits in the bottom of the engine block and runs the entire length of the block. At the front, it connects to rubber belts. These rubber belts connect the crankshaft to the camshaft and send power to other parts of the car.
At the back, the crankshaft connects to the drive train, which powers the wheels. At both ends of the crankshaft are seals, called o-rings, which keep the oil that your engine needs from leaking out.
The crankshaft sits inside the crankcase, which is under the cylinder block. It protects the crankshaft and all of it’s connecting rods from harmful external objects. The bottom of the crankcase contains an oil pan where all of the oil is stored.
The oil pump is inside the oil pan and serves to pump oil through a filter so it can be injected into the crankshaft. The oil keeps all of the components of your engine running smoothly and provides the lubrication it needs to move. After it returns to the oil pan, it starts over again.
There are balancing lobes along the crankshaft that serve to balance the crankshaft and prevent it from wobbling, which would cause damage to your entire engine. There are also main bearings along the crankshaft that give the crankshaft a smooth surface to spin inside the engine block.
The brain of the engine is the camshaft, controlling how the valves open and close. The camshaft works with the crankshaft to time the opening and closing of the intake and outtake valves. This leads to optimal performance of your engine. The lobes that run across the camshaft control this timing and are called cams.
The camshaft extends across the top of the engine block opposite of where the crankshaft connects to the pistons at the bottom. Inline engines use one camshaft to control all of the valves while V-shaped engines use two, one for each side of the V. Some V-shaped engines have two camshafts in each cylinder bank for a total of four.
The timing belt or chain holds both the crankshaft and the camshaft in the same position during operation. If at any time, these two components get out of sync, the engine won’t work. As we’ve already discussed, they work closely together to ensure optimal performance. Sometimes your timing chain can skip a gear cog, causing the engine to stop working.
The valvetrain controls how the valves operate. It’s a mechanical system that mounts on the cylinder head. It contains rocker arms, lifters, pushrods, and valves.
Your valvetrain consists of intake valves and outtake valves. They do exactly what their name suggests. Intake valves work to bring in the appropriate amounts of air and fuel needs to create combustion in the combustion chamber. Once the explosion happens, exhaust is created. The outtake valves allow the exhaust to escape.
Most cars have one of each valve per cylinder. High-performance vehicles have two of each per cylinder. Some manufacturers use the two-valve-per-cylinder model in their non-high-performance models as well. In rare occasions, there are two intake valves and one outtake valve per cylinder. Multiple valves help the engine to breathe better, which increases performance.
The cams on the camshaft touch rocker arms, which are like levers. When the cams raise one end of the rocker arm, the other end pushes on the valve stem, which opens the valve to let air into the chamber or let exhaust out. It looks much like a see-saw.
Pushrods and Lifters
In cases where the cams don’t directly touch the rocker arms, pushrods and levers are used to open the valves instead. A perfect example of this is an overhead valve engine.
Your pistons need a mix of fuel and air to create the combustion that powers their movement. Prior to 1980, carburetors supplied fuel to the combustion chamber. However, all cars today use fuel injectors to inject fuel into the combustion chamber. There are three types of fuel injectors.
Direct Fuel Injection
Each cylinder has its own injector, spraying the fuel directly into the combustion chamber and timing it just right for adequate combustion.
Ported Fuel Injection
These types of fuel injectors spray the fuel into the intake manifold instead. This manifold is right outside of the valve, so when the valve opens, fuel and air enter into the combustion chamber at the same time, again timing it just right for the combustion needed.
Throttle Body Fuel Injection
These systems work similarly to how carburetors used to. There is only one fuel injector instead of one for each cylinder. The fuel is mixed with air in the throttle body before it is distributed to each intake valve, which then opens to release it into the cylinder.
Each cylinder has a spark plug which ignites the compressed air and fuel when it sparks. This causes the combustion that powers the pistons.
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The Four-Stroke Cycle
Now that you know more about the parts that make up the engine, you’re ready to learn about how they work together to power the car. This process is called the four-stroke cycle, or Otto Cycle, and was invented by Nicolaus August Otto in 1861.
A stroke is one complete movement of the piston from top dead center to bottom dead center. You can also use the word “stroke” for the distance from BDC to TDC. A single stroke moves the crankshaft half of a revolution. The four-stroke cycle rotates the crankshaft twice and then starts again.
Step 1: Intake Stroke
First, the piston moves downward in the cylinder, which sucks air into the cylinder through an open intake valve. At the same time, the fuel injector sprays fuel into the cylinder. The perfect mixture for creating balanced performance, economy, and emissions is 1 part fuel to 14.7 parts air.
Throttle body fuel injection and old carburetor systems carry fuel to the air stream through the intake manifold to the intake port during this step. Multiport fuel injection systems have an injector for each cylinder, which can inject fuel with much more precision during this step. The exhaust valve will remain closed while the injectors inject the fuel directly.
Step 2: Compression Stroke
The intake valve closes and the piston moves back up in the cylinder. This compresses the air and fuel mixture. Because the valves are closed, the temperature and pressure of the mixture rise. A gasoline engine compression ratio is 9:1. The crankshaft has completed one rotation.
Step 3: Combustion Stroke
This step is where the power is and is sometimes called the power stroke. At the top of the piston’s movement, the spark plug ignites the mixture, which results in combustion and pushes the piston back down. When your engine is idling, these things happen five times every second in each cylinder while in a running engine it happens more than thirty times every second.
Step 4: Exhaust Stroke
When the piston reaches the bottom of its stroke, the outtake valve opens, and the piston moves back up, forcing the exhaust out. This makes room for the next cycle of fuel injection. Then the piston moves back down as part of the intake stroke again. The engine has now completed a full four-stroke cycle and the crankshaft has rotated twice.
This process is happening in each cylinder simultaneously thousands of times per minute, resulting in enough power to move your car.
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Other Engine Designs
Most cars make use of the four-stroke system, there are other types of engine designs used in cars. With changes in environmental, economic, and political conditions, there has been an increased demand for modifications to existing designs. Materials and technology continue to improve, which means more engine changes are starting to occur.
Two-Stroke Cycle Engines
This type of engine is still powered by reciprocating pistons. However, there is no valve train, which means that your fuel and air mixture, as well as exhaust, are managed by intake and exhaust ports that the piston uncovers as it moves up and down.
There is also no pressurized oil delivery because it requires the crankcase to deliver fuel. Oil is then delivered in small amounts with the fuel. Without the heavy valve train component, two-stroke engines can produce a lot of power for their size.
They have been used for a long time in small vehicles like motorcycles, boats, chainsaws, lawn equipment, and even small aircraft. In fact, while the United States imports some two-stroke engine cars, a lot of heavy-duty diesel engines are two-stroke engines as well. The trade-off for a lightweight engine with so much simplicity is a rise in emissions and lower fuel economy.
First, the spark plug fires before each downstroke of the piston. As the piston moves down, it delivers power and both the intake and exhaust ports are covered. While this happens, the downward motion of the piston pressurizes the crankcase for the next air and fuel charge.
The built-up pressure forces the reed valve to close and the downward moving piston uncovers the exhaust port so exhaust can escape. The piston continues to move down, uncovering the intake port, and momentarily, both ports are open to allow extra air to push the remaining exhaust out.
The piston then travels up again, covering the ports and creating a vacuum and opening the reed valve to pull in the next charged mixture from the crankcase.
Diesel engines are also reciprocating piston designs. They are used in some passenger cars and trucks and they operate on the four-stroke or two-stroke cycle. However, there are some key differences between gasoline and diesel engines.
The primary difference is that diesel engines use heat to ignite the fuel instead of a spark. That means a diesel engine must produce an extreme amount of heat to ignite the fuel. The pressure that a diesel engine creates when compressing the mixture is roughly twice that of a gasoline engine, meaning diesel engines are much stronger and heavier than gasoline engines. They are built with steel sleeves in their cylinders to help them withstand the extra heat and pressure.
Diesel engines also must have fuel injectors that deliver the fuel directly into the combustion chamber at the right time. If it were delivered at the same time as the air, they would ignite too early. The pressure of the fuel inside the injectors must also be very high to overpower the pressure in the chamber.
The other main difference between gasoline and diesel engines is the type of fuel they take. Diesel fuel is a type of oil. It is heavier, thicker, and less volatile than regular gasoline. On the other hand, Diesel fuel runs leaner and more efficiently. However, the drawback of a lot of combustion is a lot of exhaust, which is one of the obstacles to using them in more passenger vehicles.
This is one of the only types of a car engine that is currently mass-produced but does not contain a reciprocating piston design. This design uses fewer moving parts and the combustion in the chamber directly causes the rotor rotation.
These types of engines are smooth and powerful, operating at a higher number of rotations per minute. Starting in 1995, one of the engineering challenges with rotary engines was sealing the combustion chambers to meet current emissions standards. However, things have since improved and the rotary engine has again been in use since 2003.
Engines are classified in many different ways, and one engine can fall into multiple categories based on design characteristics or operation. Some of these classifications include:
- Design – two-stroke, four-stroke, rotary, diesel
- Number and shape of cylinders – V6, V8, I4
- Displacement (size) – 5.0 liter, 250cc
- Valve train type or number of valves – 24-valve, pushrod, overhead cam
- Ignition type – compression, spark, spark distribution system
- Cooling system – liquid, air
- Fuel type – diesel, gasoline, propane
We’ve already discussed engine design, cylinders, valves, ignition types, and fuel types above, but let’s quickly address what some of these other classifications mean.
Engine displacement refers to the size of your engine. It’s the total volume of all cylinders. It is typically measured in liters or cubic centimeters. The diameter of each cylinder is called its bore. If you know the bore of each cylinder and the length of the piston stroke, you can calculate the displacement.
Cooling System Type
All engines are either liquid-cooled or air-cooled, but most use liquid. Air-cooled engines are more commonly found in automobiles or equipment where the engine has access to open air like motorcycles or lawn mowers, although they are sometimes used in cars. Air-cooled engines run at a higher temperature and they can’t maintain a constant temperature. They typically have more emissions problems than liquid-cooled engines.
Liquid-cooled engines, or water-cooled engines use a pump to circulate coolant through the engine. They use a thermostat to keep an ideal operating temperature and can control the flow of the coolant between the radiator and the engine. Coolant is normally half water and half antifreeze. The mixture keeps the engine temperature under control and also prevents freezing, boiling, rust, and corrosion.
Torque and Horsepower
Now that you know how an engine works, what types of engines there are, and the basic characteristics that identify them, you are ready to learn about torque and horsepower. These two things are a direct result of the power that your engine produces and they are what will deliver the power your car needs to move.
Torque is measured in pound-feet but can be more casually expressed as foot-pounds instead. Foot-pounds are a measure of work rather than force, but either makes sense. Torque is the twisting force your engine has. Your engine’s cylinders create power that turns the crankshaft. This movement delivers torque to your drive train, which transmits power to the wheels.
Horsepower refers to the rate at which your engine can produce torque. Horsepower is measured by the amount of work it takes to lift 550 pounds one foot off the ground in one second. Neither torque nor horsepower directly refers to how fast your car will go, but they do tell you how much power it has.
However, you can usually assume that more horsepower will deliver more speed in a vehicle of roughly the same size, though there are other factors at play here. More torque is available at lower rotations per minute, meaning that torque is a key player in lower gears while accelerating. More horsepower is available at higher rotations per minute.
It may be helpful to look at some definitions. Energy is the capacity to do work. Engines perform the work that used to be done by horses. Work is the result of the action of force over a distance. The measurement for work is foot-pounds.
Given these two definitions, torque refers to the ability of your crankshaft to perform work. Power is how fast this work can be accomplished. Horsepower refers to the amount of power needed to lift 33,000 pounds one foot in the air over the course of one minute.
Simply put, torque is the capacity to do work and power is how quickly the work can be done. To make power, an engine either needs to generate torque, operate at a higher number of revolutions per minute, or do both.
What’s the Application When it Comes to Engine Performance?
Well, this is where it gets complicated. A certain car may be able to produce over 700 horsepower, but only at 6000 rotations per minute. It doesn’t make that much power while idling. And it only makes a little less than that 700 horsepower at the redline, while the maximum torque is delivered at only 4000 RPM.
Accurately quantifying this torque and power requires the use of a dynamometer. A perfect engine will produce enough torque at lower RPM but sustain the same output through the redline. The torque produced is proportionate to the air flow through the engine. The more air your engine can pump, the more torque it will produce, which is where superchargers and turbochargers come in, but that’s a conversation for another day.
Other components like cooling and lubrication have to be tough enough to handle this load and are needed to produce a proportional amount of power. When you begin to pump air through an engine at high RPM, the production of power becomes a beautiful form of art.
So, torque and horsepower are very closely related but don’t do the same thing. So which is better? Well, neither really. They have to work together in the right capacity to produce the performance necessary for each vehicle. While torque is critical to the engine’s operation, horsepower is what makes a good engine great.
By now, you should know a lot more about engines than when you started reading. It’s a complex feat of engineering and there’s much more to their operation than the elements listed here. Every car has multiple systems that are all interrelated and are necessary for efficient operation.