Introduction to 4 Stroke Internal Combustion Gasoline Engines
I know that seems like a lengthy title, but I had to filter expectations a little. Engines are a very diverse topic with many categories and differences, in this guide we'll be focussing on the ones found in the 3000GT, Stealth and GTO.
Describing an Engine
Engines can be described in a number of ways, let's take a look at a few of them.
- Engine Configuration
- This describes the layout of an engine, more specifically that of its cylinders. Common layouts include inline (all cylinders in a line), V (cylinders arranged in a V shape), W (two V shapes stuck together) and boxer/horizontally opposed (cylinders facing away from each other). Our cars are equipped with a V6 (V shape, 6 cylinders - 3 on each arm of the V).
- Engine Displacement
- This describes the total displacement of all cylinders in an engine. A cylinder's displacement is essentially the difference in volume of a cylinder between when the piston is at the bottom versus the top. Our engines have a factory claimed displacement of 3.0L (actually 2.972L).
- Engine Orientation
- This describes the way the engine faces in the engine bay. The engine can either be longitudinal (the front of the engine facing the front or rear of the car) or transverse (the front of the engine facing the left or right of the car). Our engines are mounted transversely.
Core Parts of an Engine
Engines have many parts that must work together in order for the engine to produce power, let's examine some.
- The crankshaft serves as the primary rotational body of the engine. As it spins, pistons on their power strokes provide it additional rotational energy, allowing it to transfer that energy to pistons on their compression strokes.
- The camshaft(s) serve as secondary rotational bodies for the engine, typically tied to the crankshaft through a timing belt or chain. As they rotate, their eccentric lobes (cams) smoothly open and close the cylinder valves.
- Pistons serve as mobile "bottoms" of each cylinder. As the crankshaft spins, it moves the pistons up and down which creates pressure (compression) or vacuum inside the cylinder at the appropriate time.
- Connecting Rod
- Connecting rods serve to connect each piston to the crankshaft.
- Valves serve as pathways into and out of the cylinders, typically for the exchange of gasses (air in, exhaust out).
- Spark Plug
- Spark plugs serve as the ignition source of the air/fuel mixture in the cylinder.
- Fuel Injector
- Fuel injectors serve as the entryway for fuel into the engine, and are capable of misting a very precise amount of fuel.
- Water Pump
- Water pumps use the rotational energy of the crankshaft (typically) to force coolant through the engine, which keeps it from exceeding its thermal limits.
- Cam / Crank Position Sensors
- Cam / Crank position sensors serve to tell the engine control unit where a given cylinder is in its power cycle, allowing it to administer spark and fuel at the correct time.
Strokes of a 4 Stroke Engine
4 stroke engines like those in most cars must complete two full rotations to complete a power cycle for a given cylinder. Each rotation is composed of a piston upstroke and downstroke, and each of the 4 serves a different purpose. Let's take a quick look.
- Intake (First Rotation, Downstroke)
- The piston moves down, creating vacuum in the cylinder and drawing air in through the intake valve. Fuel inejctors mist fuel into the cylinder to mix with the air.
- Compression (First Rotation, Upstroke)
- The piston moves up, compressing the mixture of air and fuel.
- Power (Second Rotation, Downstroke)
- The piston is propelled down by the explosion of the burning fuel.
- Exhaust (Second Rotation, Upstroke)
- The piston moves up, forcing the exhaust gasses out of the exhaust valve.
Accessory Parts of an Engine
There are many parts of an engine that aren't required for the engine to run, but either help sustain the motor long-term or provide energy to other systems of the vehicle. Let's examine some of those.
- The starter consumes battery power (the most of anything on the vehicle) to generate rotational energy in the crankshaft until it becomes self-sustaining.
- Probably one of the most important accessories of a motor in terms of drivability, the alternator charges the battery (using rotational power from the crank transferred by a belt) to recover from the drain of starting, and supplies power to everything else once the engine is running. Without a functional alternator, the vehicle will stall out relatively quickly and be unable to restart without adequate power.
- Harmonic Balancer
- Sometimes called a crankshaft pulley, the harmonic balancer helps to reduce small inequalities in the forces generated while the engine is running.
- Power Steering Pump
- Without going into too much detail, a power steer pump transforms the rotational energy of the crankshaft (transferred by a belt) into fluid pressure for the power steering system.
- Air Conditioning Compressor
- Without explaining how air conditioning works, the air conditioning compressor uses the rotational energy of the crankshaft (transferred by a belt) to compress a refridgerant gas to the point where it becomes a liquid.