How to Change Compression Ratio? (Step-by-Step Guide)

Changing the compression ratio is an excellent idea for several reasons. First, assuming that the added compression is not excessive, adding compression is the best way to improve power while also improving efficiency. For this reason, you may wonder about what compression ratio means and how you can change it. So, you may ask:

How to change the compression ratio? You can change the compression ratio in an engine by either altering the swept volume or the clearance volume. The simplest option is to change the clearance volume. You may change the thickness of the cylinder head gasket without the piston colliding with the cylinder head or any other components.

Before we dive deep into how you can change your engine’s compression ratio, you first need to understand what compression ratio means and how it can affect your engine. It’s an essential step since the compression ratio plays a vital role in your engine’s performance.

In this article, you’ll see an in-depth take on the compression ratio and how it can affect your engine. It will also help you understand the effects if you increase or increase such. This way, you’ll get a sense more about what you can do to your engine to improve its performance and efficiency.

Without further ado, let’s get into it!

How to Change Compression Ratio

What Is the Compression Ratio in an Engine?

A compression ratio is a ratio in which the most significant cylinder volume is compressed into the smallest cylinder volume. 

It is the volume of the cylinder when a piston is to the bottom, compared to up. You can see the compression ratio written down and expressed as a percentage. For instance, a 9:1 compression ratio engine would be referred to as “nine to one.”

In general, these ratios are the typical ones you can find in engines:

  • Higher compression ratio: 10.6
  • Lower compression ratio: 8.6
  • Baseline compression ratio: 9.6

A higher compression ratio sounds better, and it is. However, while you can increase your engine’s compression ratio, there’s a limit to how much you can adjust. The reason is that engines also have a specific limit.

The bottom line is that a more excellent compression ratio implies the engine gets more work done with the same quantity of fuel. So this one is good both in terms of power and miles a gallon.

With this in mind, you may wonder how you can increase your engine’s compression ratio. 

How to Increase Compression Ratio?

If you want to increase your compression ratio, you need to increase the piston’s force when the combustion starts. In general, you can get more force when the piston gets higher in the bore while the combustion happens.

The best way to increase the compression ratio is to increase the force from your piston. However, it will also create more pressure, a higher thermal effect, and whole other factors to consider. 

Thus, it would be best to get an expert’s advice so you can have your engine checked on how much adjustment it can take.

When you increase the compression ratio, the piston pushes higher in the bore, the TDC, or the top dead center. As a result, you’ll get additional force for an expansion stroke. Simply put, you’re getting extra force while maintaining the same fuel consumption.

In general, you can get better engine performance if you can get the quench area tighter. Now, one thing to note is that the increase in compression ratio depends on the capacity of your engine.

What Does Increasing Compression Ratio Do?

In simple terms, an increase in the compression ratio improves your engine’s performance. It does so by increasing the work it can do while consuming the same amount of fuel.

As a result, you can get better fuel efficiency and a more powerful engine. However, you need to note that there are limits to how much you can increase.

In general, a high compression ratio engine indicates that a given amount of air and fuel in the cylinder is compressed into a considerably smaller area than a lower compression ratio engine.

The output becomes noticeable since it provides better power despite maintaining the same fuel consumption.

Does High Compression Make More Power?

Yes, high compression does make more power. However, it also comes with several effects. To explain better and more in-depth, you can take it this way.

The first thing you need to look at is engine power. Engine power happens when the combustion chambers exert pressure or force on the piston. Then, the piston gets pushed down the cylinder as the expansion stroke happens.

In general, you can get more force when the piston gets higher while the combustion process happens. As the compression ratio increases, the piston reaches a higher place at the top dead center. Thus, it creates an additional force without consuming more fuel.

In short, a high compression makes more power. However, this fact isn’t all there is to know about compression ratio.

compression ratio change

What Happens If the Compression Ratio Is Too High?

There’s a reason why you won’t see any engine with a super-high compression ratio. When the compression ratio is too high, an engine would be prone to a lot of risks. 

For instance, try to imagine having a 50:1 compression ratio. Such a high ratio isn’t something the metal and the engine can withstand. 

High ratios tend to release high amounts of stress. As a result, your engine will likely blow or explode with such pressure.

In short, a higher compression ratio might give extra force, but having too high means your engine may not be able to endure it.

How to Lower the Compression Ratio?

Suppose you want to lower your engine’s compression ratio. In that case, you can do so by removing the material inside the piston’s top of the cylinder’s head.

As you do so, you can equally increase both volumes. Thus, you also decrease the compression ratio.

Another thing you can do is to have a thicker gasket. Having such can reduce the compression ratio, but only by a small percentage.

It’s the easiest method to reduce compression. However, the downside is that the engine will be more prone to head gasket failure. Moreover, you won’t have that much of a gain if you lower your compression.

Thus, it’s ideal only to do so when you’re having problems with high compression and you need to lower it down.

Is a Higher or Lower Compression Ratio Better?

In general, a higher compression ratio is better than the lower one. However, it depends on the type of engine you have and how much pressure it can take.

For instance, smaller engines will do better with lower compression. They may start having issues if you alter and increase compression.

On the other hand, bigger and better engines designed for extreme work would consume more fuel while having a poor performance if they run with a low compression ratio.

The compression ratios are generally between 8:1 and 10:1. A more excellent compression ratio, for as from 12:1 to 14:1, indicates more efficient combustion. Higher compression ratios and combustion efficiency resulting in more power from less fuel and fewer exhaust emissions.

Best Compression Ratio

The best compression ratio depends on the type of engine you have. In general, you can see compression ratios ranging from 8:1 to 10:1. 

You can also see higher compression ratios ranging from 12:1 or even 14:1. Such ratios mean the engine gets a higher combustion power. 

In simple terms, a higher compression ratio means more power while consuming lesser fuel. Moreover, these engines with high compression generate fewer exhausts.

Of course, a higher compression ratio doesn’t mean it’s the best. The best ratio will always be relative to the capacity of the engine. If you’re looking for the baseline compression ratio, then it will be 9:6. The lower would be 8:6, and the higher would be 10:6.

As long as your compression moves around these numbers, you’ll likely get the most out of your engine.


In a nutshell, you can say that a compression ratio is a significant factor in the capacity of your engine to work. A higher ratio means more work with the same fuel, and a lower ratio means more fuel with less work. The great thing is you can change this ratio in your car, though the change you can make is quite limited.

In an engine, you may change the swept volume of clearance volume to vary the compression ratio. Changing the clearance volume is the most straightforward approach. Without the piston interacting with the cylinder head or any other components, you may adjust the thickness of the cylinder head gasket.

In the end, altering the compression ratios is usually done by mechanics or car enthusiasts who want to build race cars and those who want to push their engines to the limit. If it’s something you want to pursue, it would be best to consult an expert, especially if you will do it in your car.

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My name is Hank, and I've been in the automotive industry for 27 years. I've been working in my own auto repair shop for the last 13 years, and now I want to help you here, on my blog. Let me know if you have any questions. Read more