What exactly does 10.1:1 compression stand for

[Oneslowgs-t]

What do the numbers actually stand for

 

[farley13]

Compression: Is the amount the air fuel mixture is compressed before the spark plug ignites the compressed mixture. During the intake stroke a specific amount of air/fuel is drawn into the cylinder. At the bottom of the stroke the intake valve closes and the piston compresses the mixture. The compression makes the mixture more volitial and when ignited it will expand more quickly thus giving you power on the downward stroke of the piston. The ratio is the amount of compression that is done. If you take 10ccs of air and compress it to 1cc then your compression ration is 10:1. This is increased but changing the type of piston or closing the combustion chamber size. The typical stock 5.0L engine is about 9 or 9.5:1 meaning 10ccs of air is compressed to 1.9 or 1.95ccs on the compression stroke. The higher the compression typically means the more power you have that is until pre-ignition occurs or pinging. This is why you have higher octane in gas to stop pre-ignition. In the old days when 103 octane was use you could run 10:1 or even 11:1 compression. The typical diesel engine runs 15+:1 but this pre-ignition helps that engine burn the fuel it uses.

 

[19Eclipse90]

The ratio is the amount of compression that is done. If you take 10ccs of air and compress it to 1cc then your compression ration is 10:1

Beat through all the fluff and this is pretty much your answer.

The compression ratio (CR) is the relationship between the volume of air (or air/fuel mixture if you are so inclined to be that picky) in a cylinder at two points, the piston's lowest and highest point. If we call the volume in the cylinder at the piston's lowest point during the intake stroke V1 and the volume in the cylinder at the piston's highest point during the compression stroke V2, then the relationship is V1 = V2 * CR. Rearranged, the CR = V1 / V2 where V1 and V2 are defined above.

Also, technically the compression ratio can be written as a single number so all this 10:1, 7.8:1, whatever is unnecessary. The CR can simply be written 10 or 7.8, respectively.

In your case, you've got 10.1:1 which is the same as 10.1. That means that V1 is 10.1 times the amount of V2.