Good engine compression and what should it be

For those who are interested in the car construction, and those who do not want to look stupid in the eyes of their friends motorists, we will consider the often encountered, not understandable term, engine compression and answer the question, “What is compression and what should it be?”

Good engine compression


Before fully answering this question, let’s figure out what the compression ratio of the engine is and what it is eaten with.

Compression ratio  

The compression ratio of the engine is called the ratio of the total volume of the engine cylinder to the volume of the combustion chamber.

engine compression


What should be the compression of a working engine?

On gasoline engines, the compression ratio has a wide range and can reach from 8 to 12 units. As for diesel engines, their compression ratio is much higher and can reach from 14 to 18 units, which is explained by the design features of diesel engines. You will understand everything if you study in detail the duty cycle of a diesel engine.

measure engine compression

The degree of compression of gasoline engines directly affects the power of the engine. So why not increase it, you ask? Yes, because with an increase in the compression ratio of a gasoline engine, the engine resource sharply decreases, problems with engine operation can occur, especially when refueling with low-quality gasoline. And today, it’s not uncommon to meet low-quality gasoline at gas stations. Probably already every driver has heard cheating at gas stations.


Learn more about what compression ratio is, what compression ratio affects and how you can increase or decrease the compression ratio.

More on engine compression

Engine compression is the maximum air pressure in the combustion chamber at the end of a compression stroke; accordingly, compression is the pressure in the engine cylinder and depends on the degree of compression. If the volume is smaller, the pressure is greater, if the compression ratio is greater, then the compression is greater. The engine compression ratio may indicate the state of the engine as a whole.


That is why, when choosing and buying a car, buyers check it for a hundred, where experts conduct high-quality engine diagnostics, which includes the compression measurement procedure. The cost of measuring compression for a hundred is usually not large. Yes, and if there is a device for measuring compression, making the right measurement of compression with your own hands will not be difficult.

Reasons for low engine compression

If after measuring compression you find low indicators, you should look for the main causes of low compression: wear on the piston rings, malfunction of the valve mechanism.

How to determine why compression has fallen in the engine?

In the cylinders with low compression, inject about 20 grams of motor oil with a syringe and measure the compression again. If the compression has grown, then the problem of low compression is in the piston rings. And if the compression readings have not changed, then there are problems in the valve mechanism. Not infrequently, there are times when engine overhaul is required with low compression.

Author: delfi

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