Fundamentals of Dyno Graph Analysis

Each dyno run produces several graphs that help tuners understand how the engine behaves under load.

The most important graphs include:

• Power graph
• Torque graph
• AFR graph

By analyzing these curves, tuners can identify performance issues and determine how ECU parameters should be adjusted.

Power Graph

The power graph displays horsepower and torque relative to engine speed.

Horsepower represents how quickly work is performed by the engine, while torque represents the rotational force generated by the crankshaft.

By analyzing the shape of the power curve, tuners can identify:

• peak power location
• power drops
• turbo spool behavior

AFR Graph

The Air Fuel Ratio graph shows the fuel mixture during engine operation.

Typical optimal values include:

• 13.2 AFR for naturally aspirated engines
• 12.5 AFR for turbocharged engines

During closed-loop operation at lower RPM, the AFR typically stays around 14.7, which corresponds to stoichiometric combustion.

Dyno Graph Analysis

By studying dyno graphs, tuners can detect several engine phenomena.

Knock Phenomenon

Knock occurs when combustion happens prematurely due to excessive temperature or low fuel octane.

On dyno graphs, knock may appear as:

• sudden power drops
• oscillations in the power curve

ECUs often attempt to control knock by enriching AFR or retarding ignition timing.

Proper correction usually involves:

• adjusting AFR
• retarding ignition timing in high RPM zones

Super Knock

Super knock is a more severe form of knock that forces the ECU to cut fuel temporarily to protect the engine.

It is commonly caused by:

• incorrect ignition timing
• poor fuel quality
• turbo system leaks

Misfire Phenomenon

A misfire occurs when combustion fails in one or more cylinders.

On dyno graphs, misfires appear as large fluctuations in the power curve.

Common causes include:

• worn spark plugs
• weak ignition coils
• incorrect injector sizing
• excessive turbo boost

Lean Misfire in Turbo Engines

In turbocharged engines, insufficient fuel under boost can cause lean misfire.

This often occurs when AFR values remain close to 14.7 during full boost, resulting in unstable combustion and power loss.

Correcting the fueling strategy typically resolves this issue.

Unstable Combustion

Excessively rich mixtures can also cause unstable combustion.

In this situation, the ECU retards ignition timing to burn excess fuel, which causes oscillations in the power curve.

Adjusting AFR and optimizing ignition timing can restore stable engine performance.

Faulty Oxygen Sensor

A malfunctioning oxygen sensor can cause AFR fluctuations and unstable dyno graphs.

When the sensor sends incorrect data, the ECU cannot maintain a stable fuel mixture.

Replacing the faulty sensor usually restores normal engine behavior.

Graph Jump

In high-power vehicles, wheelspin on the dyno rollers can cause sudden spikes or jumps in the dyno graph.

This occurs when the tires lose traction on the rollers.

Using a hub dynamometer eliminates this issue by connecting directly to the wheel hubs.