Physics Behind Modern 4 Stroke Engines

We've all seen them before, the mysterious chunks of metal under the hoods of our cars. They start when we turn the key and take us where we want to go. But how does an engine work? Internal combustion engines are a very important part of everyday life. We use them in our cars, trucks, airplanes. boats, snowmachines, 4 wheelers, and heavy machinery. These pages will help familiarize you with the basic concepts of how an engine works, an understanding of engine output, and some information on how forced induction or "boost" increases power output.

Engine Basics

A very common variant of the internal combustion engine is the four stroke engine. These engines have four "strokes" for each combustion cycle. These engines are primarily used in automobiles but have recently found their way into motorcycles, boats, and even snow machines.

The four "strokes" of these engines are as follows.

1. Intake: The intake valve (on the left top of the cylinder) opens allowing fresh oxygen rich air mixed with fuel to enter the cylinder.

2. Compression: The piston is pushed upward by the flywheel's momentum compressing the air/fuel mix.

3. Combustion: As the piston reaches the top of its stroke or TDC the spark plug fires igniting the mixture. Due to the high compression of this mixture (typically around 190 PSI in a typical engine) it is very volatile and it explodes when the spark is introduced. This pusehs the piston downward and produces power.

4. Exhaust: After the Air/Fuel mix has been burnt the remaining chemicals in the cylinder (water and CO2 for the most part) must be removed so that fresh air can be brought in. As the piston goes back up after combustion the exhaust valve (right top of cylinder) opens allow...

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... 9:1 and 9.5:1) will not burn completely resulting in excess carbon buildup (this is why you SHOULD NOT use anything higher than 87 octane in a regular engine). However, in a high compression engine as are seen in high end sedans and coupes these fuels will prevent detonation and yield better power and reliability. The octane rating is the only difference between fuel grades at the gas pump so don't be fooled into thinking that "premium" gas is any cleaner or that it will make your car run any better, it will only burn differently.

Conclusion

With adequate fuel supply and boost in some form (Nitrous, Supercharger, or Turbo) it is possible to greatly increase output without having to increase the RPM range or displacement of an engine. Power levels as high as 300-400 HP can be extracted from 1.8-2.2L engines with properly designed and managed boost setups.