What does “four cylinder” mean anyway?
When you talk about cars, “cylinders” comes up often. Four-cylinder usually comes up with smaller cars and is thought to be economical but not exactly powerful. Eight-cylinder comes up around men’s wagging tails and is usually associated with power and speed. But what exactly is a cylinder and what does it do for the car?
Long story short, a combustion engine works by pushing gas into a chamber - you guessed it- the cylinder, mixing it with air and then blowing it up. Now don’t panic, the car is not going to blow up. These explosions are tiny and expertly timed (that’s another article) to make the engine work. This process repeats over and over as the cylinders move up and down. The process can be broken down into four parts:
· Intake: Inside the cylinder is a piston. The piston strokes down on a rack that moves kind of like a bicycle pedal. The downward movement draws the air and fuel into the cylinder. At the bottom of the stroke, the valve closes, holding the air and fuel inside.
· Compression: The piston then strokes up in the cylinder and compresses the mixture according to the compression ratio of the engine. Ratios range from 8:1 to 10:0 for the most part, meaning the mix is getting squashed to a tenth of it’s original volume. Ratio varies, but the point is it's getting tight in there.
· Power: The fun part. At the top of the cylinder there’s a spark plug which does just that: sparks. The spark ignites the gas and the explosion makes the compressed mixture get lots bigger. The expansion of the vapor creates enough force when it pushes the piston down the cylinder that it turns the crank shaft to move the car.
· Exhaust: The clean-up. If you behaved like I did as a child, you know blowing things up makes a bit of a mess. Vapor is no different. Your cylinder is now full of burned gas, aka exhaust. When the piston is at the bottom of the cylinder, the exhaust valve opens letting the exhaust out to the exhaust system. This is super pressurized and loud as it rushes out, sort of like the car version of a loud fart, warranting the muffler on the exhaust system. As the piston moves up the cylinder, it chases out the remaining exhaust in preparation to start the whole thing over again.
This happens in each cylinder, each at a different time. This is the firing order. Firing order and timing are a whole other topic, but the Reader’s Digest version is:Each cylinder will have fired once to turn the crank shaft two times. So more cylinders, more “pushes” per turn. Not faster, but more oomph. This is what burns your gas, so fewer cylinders may mean better fuel economy, dependent on factors such as weight. Obviously, it takes more power to push an older car made of heavy steel than a car made of newer, lighter materials.