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The Engine

The engine in a vehicle converts gasoline and air into mechanical motion and power.

Engine types

Gasoline engines come in many types. The most common are:

  • Inline four
  • Inline (Straight) six
  • V6
  • V8
  • V10
  • V12

These descriptions denote the type of engine. The number indicates the number of cylinders. “Inline” or “straight” means the cylinders are in a line and the cylinders are vertical. V describes the shape of the engine block; typically the cylinders in these blocks are at a 60 or 90 degree angle. V-shaped blocks will have the same number of cylinders on each side; three for a V6, four for a V8 and so on. There are many exceptions to the type of engine blocks. A simple Google search will provide more variations of this magnificent machine.

Determining engine size

The size of the engine is determined by the combustion volume of all the cylinders combined. This size or measurement is expressed in cubic centimeters (cc), cubic inches (cu. in.), and now more commonly as liters (L or l). Combustion volume is the amount of space inside the cylinder measured from the top of the piston at bottom dead center or BDC to the bottom of the cylinder head with both valves closed.

The vehicle emissions control label will always have the engine size printed on it. Similarly you may find the size of the engine on a plastic cover on the engine itself.

Determining front or rear wheel drive

Engines are mounted in a vehicle one of two ways. Front to back or side to side. The first denotes a rear wheel drive configuration with the exception of certain vehicles, while the latter is found in front wheel drive cars. The easiest way to tell is to look for the belts on the front of the engine. If they are towards the front of the vehicle it is most likely a rear wheel drive. If they are on either the left or right side of the engine compartment, then the vehicle is a front wheel drive.

Basic gasoline engine operation

Most gasoline engines found in vehicle today are four-stroke engines.  The names of the strokes are intake, compression, power, and exhaust. In addition to these strokes, four items need to be present. These items are air, fuel, spark, and timing. If one of these is missing, not enough, or set incorrectly the engine may not start or if it does, it may run poorly.

The intake stroke occurs when the piston of a cylinder moves down. This creates a low pressure or vacuum and pulls air into the cylinder.

As the piston moves up it compresses this air, thus the compression stroke.  Fuel is added to the cylinder before the piston reaches the apex of travel and is mixed with the air. Just before the piston reaches the top of the stroke, spark is introduced through the spark plug. This spark ignites the air and fuel mixture.

When the air and fuel mixture is ignited, this explosion forces the piston down creating the power stroke. This happens to each cylinder in a certain order. This order is known as the firing order.

On the fourth and last stroke, the exhaust stroke, the piston moves up and forces the combustion gases that are left over from the explosion out of the cylinder.


There are many systems that work together that make this whole sequence take place seamlessly. Understanding just the basic concept of how an engine works will provide a foundation on which to build your knowledge of these other systems and components.

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