·        Idle

To tune at idle and low-throttle conditions, pockets of the fuel map are done at a time. Load is added to the engine to maintain small to medium throttle openings at lower RPMs. The pulse width of fuel injector is increased as engine RPM’s also increase. Once the RPM’s begin to drop again, the injector pulse width is decreased a few percent. This method will produce good idle characteristics.

This only needs to be done for a few positions on the fuel map. The injection time can be interpolated for the sites between the tuned positions.  Additional low-throttle, decreasing load sweeps can be made to assure proper fueling, however it may be difficult to keep the lambda sensor hot enough to get meaningful readings under these conditions.

·        Full throttle

Unlike idle tuning, it is extremely stressful on an engine to maintain 80% to 100% load at 8000-13000 RPM for very long. Not only does the engine produce a ton of heat, but also the mechanical stresses resulting from this type of operation will destroy the engine in an instant if something goes wrong.

This is where the data logging of the Motec really helps. The screen capture of the Motec Interpreter software shows a full load (100% throttle) pull on the dyno. The engine is brought up to full throttle in steps of increasing load. Once the engine is at around 7000 RPM, the load is slowly released, allowing the engine to rev up.

Once a pull is made, the engine is shut off and the logged data is downloaded from the Motec box. To analyze the fuel map, the lambda sensor is compared to engine RPMs.  You can see in the picture that the engine went lean between 6000 and 7500 RPM. The fuel map is adjusted and another pull is made to verify that the changes solved the problem.

In normal operation of an engine, the engine will not make full power in first or second gear. The engine accelerates so fast in the lower gears that the engine is unable to achieve enough load to make full power. Thus, full throttle power pulls are made in 3^rd gear or higher. Regardless of the gear used, the torque that the dyno measures must be adjusted according to the gear ratio used.

·        Drivability

The last part of engine tuning cannot be done with a water brake dyno. During operation in the car, the engine does not operate at steady state conditions. Much of what makes an engine good or bad depends on how the engine deals with acceleration. An engine may make gobs of power, but unless the driver can keep the engine in the proper RPM range, the engine is essentially useless.  Furthermore, the engine must be able to deal with quick throttle movements without stalling or hesitating. This kind of tuning takes place in the car. The Motec logging functions monitor the engine operation during a run. After a run, the box is downloaded and the data is analyzed. In this way, the drivability tuning is much like tuning for full throttle conditions.