The modern car gasoline powered engine is often described as some incredibly complex piece of machinery. It is not. Every engine has a basic four stroke power cycle. You can do a lot to make this process efficient and produce a ton of power, but it is still the same process when you strip away the fluff. Let’s take a closer look.
Most modern engines run on a piston system. Yes, there are rotary and electric engines, but the internal combustion engine is still basically a four stroke piston process. Each piston is attached to the same crankshaft. This makes all 4, 6, 8, or 12 pistons in your car part of a synchronized system.
What exactly are we talking about when we say a “stroke”? A stroke is simply a movement of the piston. When a fuel and air mixture is fired by a spark club, the resulting pressure created pushes the piston down. This is a single stroke. The movement of a piston down, up, down and up completes one cycle needed to deliver power to the wheels in a car and thus gives us the “four stroke” power cycle.
The “intake stroke” is the first step. In this stroke, the piston is moving down because the crankshaft is being turned by another piston. This downward movement creates suction. The intake valves for gas and air at the top of the chamber then open to let in the fuel/air mixture called for by the electronic computer unit controlling the engine.
The “compression stroke” comes next. The turning crankshaft moves the piston back up in the chamber. This creates massive pressure. The difference between the total space and the size of this “compressed chamber” is known as the compression ration in an engine. Most modern cars have a compression ration of 8 to 1. This means the piston moves up until it is taking up 7/8ths of the chamber.
The “power stroke” is our third stroke. When the compression is maxed, the spark plug sends an electric charge across the gap at its end, known as the electrodes. This ignites the fuel and air in the chamber. Pressure is created and the piston is forced down. This delivers power to the crankshaft and causes it to turn. The turn action moves the other pistons through their non-power strokes and delivers power through the drive train to the wheels.
The “exhaust stroke” is the fourth and last step. As the name suggests, the exhaust is removed form the piston chamber. This happens when the piston starts moving up again. As it proceeds, the valves leading to the exhaust manifold open allowing the exhaust to move out and down to the catalytic convert. From there, the exhaust is passed down the car, through the muffler and out the tailpipe.
The four stroke engine is the dominant power plant we find in the world today. This may change as hybrids and electric vehicles become more popular, but the four stroke engine in one form or another will be with us for a very long time.
Dirk Gibson is with DCJAutoParts.com – where you can find the lowest prices on high performance auto parts and accessories.