How A Car Motor Works Essay, Research Paper
Have you ever gotten smoked in a stoplight confrontation by a lesser car that you should have creamed? Does your buddy with his almost stock car pull away from you in a roll on a consistent basis? Tired of losing in front of the crowds at the local strip? Does the local “Guru” who works at your friendly neighborhood speed shop intimidate you with quasi-scientific B.S. when you try to buy something. Are you running out of hard-earned money? How do you know if the mail order house phone salesman is giving you the straight scoop on that turbo kit? If this sounds like you, then this is something you should be reading!
In the weeks to follow we will explain all of the basics, starting at first base, of how to extract more power from the chunk of metal connected to the wheels. Your new knowledge can be put to good use when selecting hop up parts for your ride, helping you make good solid choices of where best to spend your hard to come by money. Coming soon, we will explain how all the popular hop up parts work, how to understand there specifications and how to pick the right parts to best fit your needs.
To understand how the latest in speed parts work, you first need to obtain a basic understanding of how an engine works! Next we will dig into the guts of an engine to see what makes it tick. Many of you will find this stupefyingly simple but some of you readers will be glad we took the time to really explain it to you!
Cars, for the most part with the exception being the rotary Mazda, are powered by what is called a 4 Stroke engine. A 4 Stroke is called that because there are basically 4 strokes to the power cycle, the intake stroke, the compression stroke, the power stroke and the exhaust stroke. We will explain those in a minute. The 4 stroke cycle is how an explosion of gasoline and air can be smoothly transferred into useable power to hurl you down the track or take you to work.
An engine has some major functional parts, the block, the crank, the pistons and the rods. These parts work in close harmony in an exacting manner to harness the chemical energy in gasoline, converting many small explosions of air and fuel into a rotary motion to spin your wheels and hurl you down the track. These assemblies when combined are called the engines bottom end or short block.
Lets start with the main parts first, the engines bottom end.
The block is the main part of the engine that contains the reciprocating components that harnesses the explosive power of gasoline. The block has bores, cylindrical holes that the pistons slide up and down in. The number of bores equates to the number of cylinders. A four cylinder will have 4 bores and 4 pistons, a six cylinder will have 6 bores and six pistons, an eight cylinder will have 8 bores and 8 pistons and so on. The block also contains passages for cooling water and lubricating oil. Blocks are typically made of cast iron but many Imports have lightweight aluminum blocks. Most popular Imports are powered by 4 cylinder engines although some sport 6 cylinder powerplants.
Pistons are cylinders of aluminum that slide up and down in the bores of the block, the top of the bores being closed off by the cylinder head (we will talk about the head later). To make driving power, a flammable charge of compressed gasoline and air contained within the bore is ignited, and the piston is forced down the length of the bore toward the open end of the cylinder, away from the cylinder head with great pressure by the force of the small explosion of the burning gas and air. This is the basic premise on how an engine works. The piston has rings, which are thin, circular, springy metal seals that fit in grooves around the top of the piston. The rings job is to help seal combustion pressure from blowing past the piston, loosing much of the power producing pressure. The rings also help scrape lubricating oil off of the cylinder, or bores walls so it does not get burned up in the cylinder. If an engine had no rings it would not be able to develop enough compression to run, as well as burn up all of its lubricating oil in just a few minutes of running.
The connecting rods job is to transfer the force of the explosion shoving the piston down the bore to the rotating crank. The pistons are attached to a dog bone looking metal rod. This is called the connecting rod. The connecting rod is attached to the piston by a pin known as the wrist pin. This is called the small end of the rod. The other end of the rod is attached to the crank. This is called the big end of the rod as the crank’s journals are much bigger than the wrist pin journals. The crank journals are bigger because the crank journal continually rotates at a high speed as opposed to the simple rocking movement at the wrist pin end of the rod. The high speed rotation requires additional bearing 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 or sleeve bearing. On typical Import motor the small end of the rod has a bronze bushing for the wrist pin that is fed by splash lubrication.
The crank in an engine is exactly like the crank on a bicycle. It transfers an up an down force, which is the pistons being forced down the bore by the fuel/air explosion, into a rotating motion that can be used to spin the wheels. The crank has off set throws, exactly like your bicycle’s crank except the rods and pistons serve the same function as your legs, by pushing the upward throw down as the piston is pushed down the bore by the explosion of fuel and air. This is what makes your car go! After the piston goes down, the crank rotates and the piston is pushed up the bore again until it reaches the top where it can be pushed down again by another explosion of fuel and air. The crank rotates on its main journals on an oil film sleeve bearing just like on the big end of the rods.
This covers the basic bottom end assembly and how it works. In our next installment we will get into the operation and function of the cylinder head and some of the other important engine subsystems.
In this weeks installment we will continue to discuss some of the engines main internal parts and how they work. It might seem boring now, but it is essential to understand the workings of these parts so when we begin to modify them, we have a better idea of what there function is.
In this installment we cover the all-important top end of the engine. The cylinder head and all of its parts are important because it controls what goes into and out of the engine. The head, like your head is the brain of the engine. Lets dig right in for this week’s lesson.
The Cylinder Head
The Cylinder head is, on most Imports, an aluminum casting that caps off the top of the block and contains the spark plugs, valves and the valve train. The head must contain the explosive force of the igniting fuel air mixture so the explosion of said mixture could only drive the piston down the bore instead of blowing out of the bores top. The cylinder head has the combustion chambers cast into it. This is the area where the valves and sparkplug are located. When looking at the underside of the cylinder head, the side that bolts to the block, the combustion chambers are the depressions that line up with the bores. It is in these chambers where, when the piston is at the top of its stroke; the fuel air mixture is ignited, kicking off the power stroke. The cylinder head also has cooling jackets filled with circulated water to help keep the combustion chambers from getting too hot.
On a modern engine the head also contains the intake and exhaust valves. The intake and exhaust valves are spring loaded poppet type valves. The springs hold the valves shut, but allow them to be opened with a push. The intake valves open to admit the explosive mixture of fuel and air into the combustion chamber. They then close to allow the engine to build up compression as the piston, driven by the crank comes up to TDC or top dead center, this is what engine builders call the event when the piston is at the top of the stroke. When the spark plug ignites the fuel air mixture and the piston is driven down, and the exhaust valves open near the bottom of the pistons downward travel, allowing the burnt waste gasses to escape to prepare the combustion chambers for the next charge of fresh fuel and air.
The valves are opened and closed by the camshaft or camshafts, which are basically rods with off center bumps or lobes on it that spins in the cylinder head at 1/2 of the crankshafts speed. The lobes of the camshaft push the valves open and closed so that air and fuel can be admitted with burnt exhaust being expelled. Sometimes the cam can work directly on the valve. Many motorcycles and racing type engines are like this. Typically the camshaft works the valves through a rocker arm, which is like a miniature teeter totter. One end of the rocker arm rubs on the rotating camshaft with the other end pushing the valves open and closed.
The engines found in imports are typically called overhead cam engines. This means that the camshaft is contained within the cylinder head on top of the valves. This is opposed to overhead valve engines like low revving, old school domestic V-8. s that have the camshaft located in the middle of the block, connecting to the valves with, lifters, long pushrods and rocker arms. Overhead cam engines are better for the typical high rpm, small displacement Import motor, because they have simpler, lighter, more direct acting valve trains. These valvetrains work better at high rpm because their lower inertial mass allows them to follow the camshaft. s lobes with more accuracy. If the engine has only one camshaft that controls both the intake and exhaust valves it is called a SOHC or single overhead cam motor. The Honda D16 that is found in the ever popular Civic and the Nissan VG30 are examples of SOHC motors.
Many Import motors have dual overhead cams, which means that there are separate cams for the intake and the exhaust valves. The advantage with this is that the 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 valve train to a minimum, which helps high rpm operation even more. Just about all of the higher performance Import motors use dual overhead cam valvetrains also known as the DOHC configuration. The Nissan SR20DE and the Acura B18C are prime examples of DOHC motors.
The Intake System
The intake system consists of the manifold, which basically is a series of pipes that connect the throttle body, which is the valve the controls the amount of air that can reach the insides of the motor, to the intake ports of the head. The throttle controls the amount of air the engine can suck in, thus controlling its speed and power. When the throttle is shut, the air is very limited so the engine must idle. When it is wide open, the engine takes in all the air it can so it can produce its maximum level of power. The manifold usually contains the fuel injectors, which are electro-mechanical valves controlled by the ECU, or engine control unit, a small computer which is the engines brain. The ECU controls the amount of fuel being injected into the engine by modulating the open and closed time of the injectors. When the throttle is fully opened, allowing the maximum amount of air possible into the engine, the ECU will command the injectors to stay open longer so they can inject a proportionally greater amount of fuel to create a bigger volume of explosive fuel-air mixture. More fuel . air mixture means a bigger explosion and more power.
The Ignition System
To get the fuel air mixture burning, the ignition system ignites the flammable mixture by firing a powerful electrical spark across the electrodes of the spark plug. The engine. s ECU controls the timing of this spark. The spark is fired as the piston has almost risen to Top dead Center (TDC) near the peak of the cylinders highest compression. This is the most efficient time to fire the spark. Usually the timing of the spark advances as the engines RPM increases. This is because at higher RPM there is less time for the combustion event to take place so it must be started sooner in the cycle to maintain proper operation.
The Exhaust System
The exhaust system is simply the tubing that directs burned exhaust gases away from the motor. The exhaust system consists of the exhaust manifold, the catalytic converter and the exhaust pipe. The manifold collects the exhaust gas from each individual exhaust ports in the cylinder head and collects them into a single pipe. This pipe leads into the catalytic converter where poisonous constituents of the exhaust gas such as Oxides of Nitrogen (NOX), various unburned hydrocarbons (HC) and carbon monoxide are converted to non-toxic CO2 and water vapor. After the catalytic converter, the gases flow into the exhaust pipe where they pass through the muffler, which reduces the noise to an acceptable level and out into the atmosphere.
Although not directly responsible for motivating your ride but nevertheless deserving an honorable mention as critical parts of a motor is the engine’s cooling and lubricating systems.
The cooling system circulates a mixture of antifreeze and water throughout the block and head keeping them from getting too hot from the continuous explosions that they are subjected to internally. The water is pumped out of the block to the radiator, which is a heat exchanger located in the very front of the car, to be cooled down and re-circulated back through the engine. A faulty cooling system can wreck a motor very quickly by letting it overheat. Although this sounds very basic, my neighbor almost ruined his motor by driving around for several days with his temperature gauge pegged, when his radiator sprung a leak. He really did not know that overheating will surely destroy an engine very quickly. The fact that his Integra still runs pretty well once he fixed the radiator is a strong testament to the bulletproofness of these engines.
The lubrication system consists of a pump which pumps oil to all of the engines bearings located on the crank, and the valvetrain. The pistons and rod wristpins usually rely on splash that is created as oil is flung off the rotating crank. One of the quickest ways to ruin an engine is to run it out of oil. My neighbors older brother almost trashed his Acura Legend’s engine by doing this once. He did not realize that periodically you must check the oil level, and nearly ran the engines 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. Don. t laugh, the only reason that I, a supposed expert, know this stuff is that it was drilled into my head by my engineer father. My neighbors father owns a restaurant and does not work on his car at all. He doesn’t work on cars and my Dad cannot cook awesome Chinese food.