They are typically used to visualize the opening time versus area and/ or lift of the following components:
- Intake port / valve
- Scavenging port / valve
- Exhaust port / valve
- Reed inlet valve
- Rotary inlet valve
They do not show the specific configuration of ports like in a port-map, which enables it to illustrate a more useful visualization of port area distribution,
This could be useful because different types of port configurations could have the same opening time and area.
In these graphs the X-axis represents the crankshaft angle (θ) in degrees, and the left Y-axis represents the open area in any square unit of measure such as cm². To discern the different types of ports each type is given a designated color.
For example (commonly used):
- Blue - Intake system
- Green - Scavenging system
- Red - Exhaust system
- Purple - Inlet valve
Kramer graphs are named after Dutch engineer H. Kramer, who is considered to have been the first to use this type of graph in a publication on the effect of port shape and area on two-stroke cycle engine performance.