How to read dyno graph
Reading the graph of the chassis dynamometer pull is not difficult. Typical chassis dyno (rolling road) graph is arranged like this: the horizontal axis shows the engine speed (or alternatively – car speed) and the vertical (or two vertical, mainly on the left and right side of the graph) power, torque and optionally other logged parameters (eg. turbo pressure, lambda, AFR, exhaust gas temperature or the rate of smoking, OBD logs etc/).
To read the dyno graph properly we must distinguish how many different measurements are on the chart. We usually have one or two measurements (if two are present - they are usually: parameters measured before the modification (reference), and the modification - (eg. measurement of performance chip tuning). If one of the measurements is presented with thinner lines - this is probably reference measurement (as happens in these dynos, which can not show more graphs in one chart). If there are more measurements, they will definitely have different colors, making it easier to distinguish.
We will discuss two examples of a dyno graph with a chassis dynamometer - companies Maha and V-tech Dynamometers. Charts from other third-party dyno manufacturers look very similarly, because they use the same pattern of data presentation.
MAHA dyno graph
Car used: Porsche Cayman. In the dyno graph we have imposed two measurements. Reference measurement (factory power) is presented with thinner lines. Power on wheels (1) is shown in blue, the power of resistance and loss (2) with a green color, then normalized engine power - that is the one that we are most interested (3) it is drawn in red and finally normalized torque (4) - orange. On the horizontal axis we have rpm of engine, while the vertical axis on the right side is for both power and torque. For example, if power is 400 hp and torque is 400 Nm - then graphs of power and torque reach exactly the same maximum level, although probably at different speeds.
Accurate data of maximum values of parameters measured are given in the table below. I marked them with appropriate numbers. You should be careful - they are in a different order than on the legend of the chart (but they do have the right colors). The rpm of maximum power is just below the power loss (but of course these are revolutions appropiate to the power drawn in red), the speed of maximum torque (4) are below the torque. Down here we have a maximum speed of rotation of engine during pull and the speed.
On the right side we have the environmental data. (5) the temperature of the environment, (6) the temperature of the intake air by the car. Temperatures (5) and (6) should be similar. The difference greater than a few degrees means poor ventilation hall measuring or falsification of the chart (if artificially „inflate” the temperature of the intake air, (eg. by giving the sensor under the hood) – DIN correction, which normalizes the graph will overestimate the result. It is also worth noting that the Maha dyno graph does not have environmental data for reference measurement as reference measurement is only a static background to chart the right. Then we have (7) atmospheric pressure. Dynamometers measure air humidity (presented above atmospheric pressure), but the effect of humidity on the results is small. On the basis of the graph is not possible to determine the date and time of reference measurement, as well as its environmental conditions, but you can ask tuner (dyno owner) for a separate print for this reference dyno test and then these missing datas in the chart will appear.
V-tech Dynamometers dyno graph
The dyno tested car is Porsche Carrera. Graph is similar to Maha dyno graph. In the graph, there are two measurements. Because with V-tech Dynamometers control softwar up to 4 measurements can be presented, they are marked with different colors. The color is shown in the table below, along with the name of the measurement. At the dyno graph we have the power of resistance and losses (2) engine power normalized (3) and normalized torque (4). Rpms at achieving the maximum power and torque are shown next to their values. Shift – it is a transmission ratio (simplifying: the speed that the car runs on the selected gear at exactly 2000 RPM). Inlet air temperature is (6), Atmospheric pressure is (7). Below are the date and time of measurement - can we be sure what conditions prevailed for all individual measurements and what was the exact date and time of measurement.