Simple Tech: Variable compression ratio engine

Compression Ratio (CR) is a simple term. It's the ratio between the maximum and minimum cylinder volume of an internal combustion engine. That means the ratio between the cubic capacity when the piston is at the bottom of the stroke (BTDC) versus when the piston is at the top of the stroke (TDC). In effect, CR, expressed as 11:1 for instance, tells you that this particular engine will compress the incoming charge (air-fuel mixture) 11 times before combustion.

As...