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Compression ratio calculator

How to calculate the Compression Ratio (CR) of your engine

by
Bartek Bartoszewicz Tuning Professional

#verdichtung

Compression ratio

The compression ratio is very important for the smooth running of an engine.

The ratio between the total displacement and the compression space above the piston (combustion chamber) is the compression ratio. The compression ratio must fit the engine design and fuel! As a rule of thumb, one could say: The higher the octane number of the fuel, the higher the compression ratio can be selected. Too high compression or bad fuel can lead to dangerous knocking. An engine with too low compression loses efficiency and becomes sluggish, since the injected fuel-air mixture cannot be burned properly.

CONTENT

1. Compression ratio calculator
2. How to calculate the Compression Ratio (CR) of your engine
3. FAQ
4. Examples of a good engine concept
5. Conclusion

Compression ratio calculator

CHOOSE ENGINE CODE:

Piston protrusion:

mm

Thickness of head gasket:

mm

DIFFERENCE:

mm

Inner diameter of head gasket:

mm

CAPACITY OF HEAD GASKETS:

cm³

Capacity of piston:

cm³

Capacity of head:

cm³

CAPACITY OF COMBUSTION CAMBER:

cm³

Stroke:

mm

Bore:

mm

CAPACITY OF ONE CYLINDER:

cm³

Number of cylinders:

Cylinders

COMPLETE CAPACITY OF THE ENGINE:

cm³

RESULT

: 1

Compression

: 1

How to calculate the Compression Ratio (CR) of your engine

Here you can easily calculate the compression of your engine. There are two ways:

Choose your engine code from the drop down menu. All values will be filled out automatically and you can „play around“ with the thickness of the head gasket. Thicker head gaskets will drop your compression ratio.
You can fill all the data manually in the grey fields. This makes sense, if your engine code is not in our list, or if you have made big changes to your engine hardware like other pistons for example.

In order to arrive at the appropriate compression later, it most makes sense to do this via the thickness (gauge) of the head gasket. For this purpose, we offer racing gaskets in 0.1 mm increments for most engines. However, please note that our gaskets are always made to order. So there may be longer delivery times. Additionally, we recommend the use of ARP bolts or studs instead of normal cap screws. The ARP bolts are much more stable against the high combustion chamber pressures and can even be reused.

Which compression should I choose?

We do not want to deal with complicated formulas here. As a rule, when tuning, we want to increase the engine power. In the case of a turbo engine, this means increasing the boost pressure. Up to a certain limit, the original compression can be maintained, only the software is adapted to the higher pressures. But if a different turbocharger comes into play, then the compression must also be adjusted downward. Otherwise, the engine would start knocking very quickly with its stock compression. Modern engines have very good knock control, which then also reduces the ignition should knock occur. The goal, however, should be to prevent this control from becoming active in the first place. So the concept between boost pressure (or filling), fuel quality and compression must fit.

Examples of a good engine concept:

1.8T (20V) engine as used in the Golf MK4 or Audi TT until year 2005:
Garrett GTX28 Turbo, 102 Octan fuel = best CR 8,5:1, max. power output with our ECU tuning: 330 PS (243 kW).

2L TFSI engine as used in the Golf MK5 or Audi A3 until year 2012:
KKK Upgrade Turbo V2 BAR-TEK, 102 Octan fuel = best CR: 9:1, max. power output with our ECU tuning 420 PS (309 kW).

2.5L TFSI engine as used in the Audi RS3 or TTRS:
Garrett GTX 35 Turbo, 102 Octan fuel = best CR 9:1, max. power output with our ECU tuning: 750 PS (552 kW).

You can see from our examples that the best compression is always different. Especially with regard to the final performance. This is also due to the different engine concepts. However, in general it can be said that a lower compression ratio is always better. So if you are not sure, ask us or have your engine professionally gauged. Of course, this is only possible if the cylinder head is not mounted. We can help you with that as well.