by Layne Ross, Clemson Automotive Engineering Student
Basic Description
With increased government emission standards, specifically the cafe standards becoming more stringent every year has forced vehicle manufactures to sub optimize performance for increased fuel economy. One of the ways to increase fuel economy is to have advanced ECU's to tightly control the combustion process and by running lean conditions (air/fuel ratio >14.5:1) to maximize thermal efficiency. Also many vehicle manufactures are downsizing the displacement and adding forced induction. With this combination becoming more popular on sports cars and heavy duty trucks this opens up flexibility to gain more power. Using aftermarket tuning system optimizes air/fuel ratio, spark timing, boost pressure, and many other engine parameters to maximize power output. Enthusiasts now have the ability to achieve more power for racing or towing more easily then ever by installing a flash tuner or piggy back tuner.:
Flash Tuners
Flash tuners are computers that usually hook up to the OBD II port. The flash tuner connects to the ECU and backs up all factor maps and installs new maps on the hard drive. A map is a 2 or 3 dimensional graph. The intersection point is referred to as the "Look up value". The most important map is the VE (volumetric efficiency) map. VE maps typically read MAP or MAF, intake air temperature and crank shaft speed sensors (engine RPM). From these engine inputs the map has calculated the engine load. The engine load is the look up value in the graph which is the fueling or pulse width signal to the injectors.
Another map that flash tuners have is the ignition map which controls the timing of the spark. Depending on the octane of the fuel, compression ratio, and IAT the ignition can be advanced or retarded to increase or decrease in cylinder pressures. Flash tuners typically offer several different maps to optimize engine performance based on engine modifications.
Piggy Back Tuners
Piggy back tuners are a computer that connects in series with the factory ECU. Piggy back tuners are similar to flash tuner but uses the factory maps. These tunes use modifiers on the input and output signals from sensors like the MAP/MAF to "trick" the engine to make more power. Piggy back systems also have capability of switching maps but in this case it is changing the signal modifiers. Typically piggy back tuners do not control the engine as smoothly because of real time calculations.
Common input sensors to ECU and piggy back tuner controlling injector output
Tuner System Features
Aftermarket tuners are not only used to increase the performance of a vehicles engine but they can also be used as a diagnostic tool to look up MIL codes. Other features include: speed delimiter, PID boost control, rev limit launch control, Methanol PWM control, gauge hijacking and data logging. Data logging is recording sensor output on a graph. The data is used to diagnose misfires or fine tune engine parameters.
Data log of a vehicle accelerating at wide open throttle through 1st and 2nd gear.
Below is a video of the installation and feature demonstration of a JB4 piggy back system on a 335I.
