Text by Mike Kojima and Arnold Eugenio // Photos and Illustrations by DSPORT Staff
DO YOU FIND THAT you're addicted to the thrill and speed of driving fast, but don't know the first thing about what's actually going on under the hood? Do you want to know more about what's happening without having to attend Auto Shop 101? Are you intimidated by the tech at your local performance shop because he's always trying to sell you blinker fluid, muffler bearings and other parts that you're not sure even exist? If you answered "yes" to any of these questions, this is where you need to start. We'll tell you all about the noisy chunk of metal connected to your wheels and a little bit about the things that make it go forward.
Knowledge is Power
In order to fully understand how the latest in speed parts work, you first need to understand how an engine works. Most cars as we know them are powered by what is called a 4-stroke engine. A 4-stroke refers to the four strokes in the power cycle; the intake stroke, the compression stroke, the power stroke and the exhaust stroke. We will cover these in greater detail in the ENGINE 2 section. For now, what you need to know is that the 4-stroke cycle explains how a mixture of gasoline and air can be ignited, combusted and smoothly converted into useable power to hurl you down the quarter mile, around a track or just take you to work.
An engine is composed of several major components; the block, the crank, the rods, the pistons, the head (or heads), the valves, the cams, the intake and exhaust systems and the ignition system. These parts work together in an exacting manner to harness the chemical energy in gasoline, converting many small and rapid combustion events into a turning motion that eventually spins your wheels and propels your car.
Block Hole, Son
The block is the main part of the engine that contains the reciprocating components that harness the energy in the gasoline. If you're looking under the hood, it's the big piece of metal that's found in the center of the engine bay that seems to have a whole bunch of other metal, wires and tubes attached to it.
The block has circular holes that pistons slide up and down in. Each hole is called a "cylinder bore". Since a cylinder bore or "cylinder" has one piston the total number of cylinders in the block is the same as the number of pistons; a four-cylinder engine has four bores and four pistons, a six cylinder will have six bores and six pistons and so on. The cylinder head is called a head because it sits on top of the block, covering the cylinders and the pistons. Some engines feature cylinders that are horizontally opposed or are in a "V" configuration. As a result, there are two heads that cover the areas on the block that have exposed pistons. For now, we just need to know that the cylinder head, or head for short, just sits on top of the block and covers each of the cylinders that have pistons in them.
The block also has a number of fluid passageways cast into it. Some of these are used to channel cooling fluid called "coolant" around the cylinders to maintain engine temperatures and to prevent overheating. The other passages direct engine oil to the moving parts to lubricate and defend against power-robbing friction. Since the block must contain tremendous cylinder pressures, manufacturers cast them out of iron for strength. Other manufacturers cast lightweight aluminum blocks for weight reduction. The aluminum blocks use a steel-alloy cylinder liner or specially-coated bores so that they have a harder surface and will provide an extended service life.
Pistons move up and down in the cylinders of the block because a mixture of fuel and air is ignited within the cylinder. The subsequent combustion rapidly expands and pushes the piston down the length of the cylinder bore, away from the cylinder head, and with a lot of pressure. That power produced in one cylinder is multiplied because the combustion events are repeated in each of the cylinders. This is the basic premise on how an engine works.
Each piston has open-ended rings of metal fitted onto them, and they are simply referred to as "rings". These are thin, circular, springy metal pieces that fit in grooves around the ring land areas at the tops of the pistons. The rings act as a seal that keep the cylinder pressure from the combusted air and fuel mixture between the head and top of the cylinder, ensuring the pressure pushes the piston down instead of pushing past it. The piston rings also scrape oil off the cylinder walls so that all of your engine's oil doesn't get burned up during combustion. There is also a corrugated ring, known as the oil ring, which allows oil to lubricate the cylinder walls so that the piston, rings and cylinders do not wear prematurely. If your pistons had no rings or rings that didn't seal very well, the combustions wouldn't be able to push down the piston with much force and your car wouldn't produce any power, if it ran at all. Also, if the rings weren't able to scrape the oil off the cylinder walls your engine would eventually run out of oil, seize up and make a whole lot of nasty black smoke from the burning oil in the process.
Pistons and Rods
The pistons are attached to a piece of metal called a connecting rod. The connecting rod's job is to transfer the force of the pressure shoving the piston down the cylinder bore to the crankshaft or "crank". Providing the link between the piston and the crank, it is understandable how connecting rods earned their name.
The connecting rod is coupled to the piston by a tube called a wrist pin. The wrist pin slides through a bore in the piston and a bore on the smaller side of the connecting rod; that area is called the small end of the connecting rod. The big end of the rod is the area that connects to the crank. The rod's big end has a removable section called an end cap or cap that allows it to be attached to the crank.
The surface area where the connecting rod pivots around the wrist pin is called the wrist pin journal. The area on the crank where the rod connects and rotates around are called the crankshafts rod journals. The crankshaft's journals are bigger than the wrist pin journals because the crank journal continually rotates at a high speed as opposed to the simple back-and-forth rocking movement at the wrist pin end of the rod. This high-speed rotation requires more surface area to prevent the rod and crank from being damaged by friction. The big end of the rod spins smoothly on the journal of the crank on a pressurized oil film that coats a soft metal sleeve bearing. On most engines the small end of the rod has a bronze bushing for the wrist pin that is fed by splash lubrication. On some engines the wrist pin is fed from oil scraped by rings from the cylinder walls through a passage from the oil ring groove called a pin oiler. It's rare, but there are some instances where the wrist pin is fed pressurized oil from the rod bearing from a hole drilled through the length of the rod from the rod's big end.
The crank in an engine is very similar to a bicycle crank. The up-and-down force of you pedaling is exactly like the up-and-down force of the pistons moving up and down the bore. In a car engine, instead of the energy of your legs pushing on pedals to create the force it's the combustion in the cylinder and pressure acting on the piston that creates the energy. If you look at the picture, you'll see the crank has offset throws exactly like a bicycle crank so the rods and pistons serve the same function as your legs. On a bike, when you pedal downwards your bike goes forward and the offset throw comes upward on the other side. Similarly, when one piston is pushed down by the fuel/air combustion, it turns the crank and pushes another piston up, ready for the next combustion. This is what makes your car go forward.
The crankshaft is attached to the block with pieces of metal called main caps. The crank is actually clamped to the block, not attached, with more sleeve bearings (called main bearings) to help lubricate the crank's journals. The main journals also have holes in them that allow pressurized oil from the engine oil system to lubricate the journal and bearings.
The Head Honcho
As mentioned earlier, the cylinder head is a big piece of metal that attaches to the top of the block and covers the cylinders where combustion occurs. Usually constructed from aluminum, the head also contains the spark plugs, valves and the rest of the valvetrain (valve springs, retainers, camshafts).
The head(s) have to be torqued down to the block in order to contain the rapid-expansion of the ignited fuel/air mixture without distorting, separating or blowing completely off of the top of the block. When the head is torqued down to the block, it creates an area atop each cylinder where combustion energy is released and focused on the piston. This area is called the combustion chamber. If you look at the side of the cylinder head that bolts to the block you'll see the combustion chambers as the spaces in the head that line up to the tops of the cylinder bores. Visible within each chamber are the tip of the spark plug and the flat parts of the valves. It is in this combustion chamber that the spark plug creates an electrical arc which ignites the air/fuel mixture.
The head also has passageways cast into it that allow coolant or oil (depending on what kind of passageway it is) to circulate through the head to help it keep cool and lubricated as well. In between the head and block you will find a piece of metal or composite material that has areas cut out for each of the bores and every one of the passageways that run from the block to the head. This sandwiched piece is called the head gasket.
Valves: The Gateways In and Out
The cylinder head also contains the intake and exhaust valves. The intake and exhaust valves are metal pieces that resemble golf tees. The valves act as doorways for incoming air and fuel and outgoing exhaust gasses, respectively. During the 4-stroke process, the intake valves open to allow the fuel/air mixture into the combustion chamber then closes as the piston rises to compress the mixture. After the mixture is ignited and burns, the piston is pushed down into its bore. On the piston's way back up, the exhaust valves open to let the burnt gasses out and then closes in preparation for its next turn in the engine cycle. In order to open the valves, the engine has metal sticks called camshafts that have special bumps (lobes) used to lift the valves open. The cams are turned by a belt or chain that connects the spinning crank to the cam gears; this is what's called the timing belt or timing chain. Some camshaft lobes push directly on the valves to open them, but most street-driven car engines work indirectly through a rocker arm. A rocker arm is essentially a miniature see-saw; one end of the rocker arm is pushed up by the camshaft lobe which makes the other end push down on the valve tip to open the valve. Valve springs are literally springs attached to the valves that help keep them closed when they're supposed to be closed.
The Crazy Train
Most modern engines have a dual overhead cam (DOHC) valvetrain which means that the intake and exhaust valves have their own camshafts. The advantage of having separate camshafts is that each cam can be placed very close to the valve, allowing the cam's lobes to either work directly on the valves or through a very small rocker arm. This reduces the inertial mass of the valvetrain to a minimum which aids high-rpm operation even further. Almost all modern high-performance engines use DOHC valvetrains in order to maximize the amount of available high-rpm power. The Mitsubishi 4B11 found in the EVO X and the Mazda MZR 2.3 DISI found in the MAZDASPEED3 are prime examples of current high-performance DOHC motors.
Every Breath You Intake
The intake system refers to the components of the engine that get air and fuel into the combustion chamber. The intake manifold is essentially a series of pipes and chambers that connect the throttle body to the intake ports on the head. The throttle body, which connects to the main opening of the intake manifold, is a piece of metal that holds a flapper-type door called a throttle plate. Opening and closing this plate controls the amount of air that's coming into the engine. So when you step on the "gas" pedal on a modern fuel-injected engine, you're really just opening the throttle plate to let in more air. When the throttle is shut, the incoming air is limited so the engine speed is slowed down. When the throttle is wide open, the engine takes in as much air as possible, raising the engine speed and allowing it to produce the maximum level of power.
On most applications, the intake manifold holds the fuel injectors. These injectors are electro-mechanical valves that are commanded by the engine control unit (ECU), a small computer that acts as the engine's brain. The ECU controls the amount of fuel being injected into the engine by constantly changing the amount of time the injectors stay open or closed. Under cruise or light throttle conditions, the ECU maintains the proper ratio of fuel being injected relative to the volume of incoming air to produce the lowest possible exhaust emissions and keep the catalytic converter working efficiently. When the throttle is wide open and allowing the maximum amount of air into the engine, the ECU will command the injectors to stay open longer so they can inject a greater amount of fuel relative to the amount of incoming air. This creates a greater volume of combustible fuel-air mixture, which in turn means more power output.
The part of the intake system that's most familiar to the general public is the series of pipes and chambers that lead cooler air from outside the engine bay through a filter and eventually to the throttle body. In general, the complete intake system encompasses all of these parts.
3, 2, 1, Ignition
To get the fuel/air mixture burning, the engine has an electronic ignition system that ignites the fuel/air mixture by firing a powerful electrical arc across the electrodes of the spark plug. The engine's ECU controls when the spark is initiated, which is termed spark timing.
In order to have enough voltage to create a strong enough spark in the combustion chamber, a car's ignition system usually includes an energy transformer called a coil. The coil converts the 12-to-14 volts supplied by the car's charging system into a high-voltage current (15,000-to-35,000 volts) that flows from the coil to the distributor. The distributor is the unit that sends this voltage through spark plug wires to the correct spark plug to fire at the appropriate time.
More and more engines are relying on a distributorless ignition system (DIS). DIS designs place individual coils on each spark plug, doing away with the need for a distributor. These systems can be easily identified by the short length or complete lack of spark plug wires. Sometimes, a sticker or stamp will identify the engine as having a distributorless ignition system.
The exhaust system is simply the tubing that directs burnt exhaust gasses away from the engine and, usually, out of vehicle's back side. The complete exhaust system consists of the exhaust manifold, a catalytic converter (on pollution controlled vehicles), exhaust piping and a muffler. The exhaust manifold collects the exhaust gasses from each of the exhaust ports in the cylinder head and routes them into a single pipe called a collector. On non-turbo charged engines, this entire assembly or unit is called a header. If an engine has a single cylinder head, then there is only one header. If it has dual heads, such as those found on V6 or V8 engines, there are two headers – one for each exhaust port bank on each cylinder head. If so equipped, the header leads into the catalytic converter where the amounts of hydrocarbons, oxides of nitrogen and carbon monoxide are reduced. After the catalytic converter, the gasses flow into the exhaust pipe where they are routed to the muffler. The muffler's job is to reduce noise to an acceptable level before directing the gasses out into the atmosphere.
Cold and Slippery
The cooling and lubrication systems of the engine are not directly responsible for moving your car forward, but they do deserve an honorable mention since they are still necessary and critical systems that keep your car's engine alive.
The cooling system circulates a mixture of antifreeze and water, known commonly as coolant, throughout the block and cylinder to deal with the waste heat of combustion. The water is pumped out of the block to the radiator, which is a heat exchanger often located at the front of the car. The radiator allows the water to cool down, after which it is re-circulated back into the engine block. Be sure to properly maintain an engine's cooling system as a faulty one can destroy a motor very quickly by allowing it to overheat.
The lubrication system of an engine consists of a pump and a closed-line system that delivers oil to all of the areas that require it, specifically to the crank and rod bearings as well as the valvetrain. The pistons and connecting rod wrist pins usually rely on oil that is flung off the fast-rotating crank for lubrication. The oil pan, where all of the oil pools and collects before being drawn back into the engine by the oil pump, sometimes partially submerges sections of the crank, which allows it to splash and slosh oil around to other engine components that require lubrication.
Besides overheating an engine, another quick way to ruin an engine is to run it out of oil. My neighbor's older brother almost trashed his Acura's engine by doing this. He did not realize that he was supposed to periodically check the oil level and he ran he engine's oil supply down to nothing. Fortunately, he asked me what the oil pressure warning light meant and we caught the low oil level before any damage was done.
Wrapping It Up
Don't laugh – that last story and all the information we've presented here about how engines work may seem like common sense to some of you, but for those that read this far and learned something, this might all be new information. Don't be discouraged though; the only reason I know this stuff is that it was drilled into my head by my engineer father. My neighbor's father owns a restaurant and didn't teach his son, my friend, anything about cars. By the same token, my engineer Dad cannot cook awesome Chinese food no matter how hard he tries.
This article was submitted by DSPORT MAGAZINE. To find this and more excellent articles, check out DSPORT MAGAZINE ISSUE #101 or call us at 714-539-0280 to orders yours today.
For everything you need to know about Chassis, Suspension, Fuel Systems, Electronics and a whole lot more, check out: https://dsportmag.com/browse/table-of-contents