LNF Learndown Feature Explained

For the past 10 years that the LNF has been on the market with the Pontiac Solstice GXP, Saturn Sky Redline, Chevy Cobalt SS, and Chevy HHR SS there has been a lot of talk regarding the factory ECUs learndown feature. Up until this point, there has been very little public knowledge about the topic outside of casual discussion. Here is some information on the Learndown Feature as explained by our techs at RPM-Motorsports.

The factory tune in the LNF ECU is set to calculate the desired amount of Airflow allowed in order to achieve a predetermined amount of torque output. This ECU uses a complex calculation of wheel speed, rpm, throttle position, and other factors in order to internally calculate the amount of torque being output by the motor. When the motor is sensed to be producing less than the expected amount of torque (such as bogging in the wrong gear or going up a hill) the ECU can compensate by adding more airflow (i.e. Boost) until it reaches it's tuned limitation of airflow. Inversely, when doing a burnout the ECU estimates that the engine is producing more torque than expected and it will therefore reduce the amount of commanded airflow, which will reduce the boost pressure.

Now, airflow does not always have to come in the form of boost. Boost is actually a byproduct of airflow restrictions in a certain airflow rate. For Example: It could be entirely possible to move 32 pounds of airflow at 19psi, and then upgrade your charge pipes and other parts and then move that same 32 pounds of air at 17psi. In an ECU that was boost referenced, the engine would then still output 19psi and end up moving more than the 32 pounds of airflow.

The E69 ECU used in the LNF is quite different. This ECU uses airflow calculations to dictate boost pressure and torque output. In the above scenario the LNF ECU would just congratulate you for your improved efficiency by reducing your commanded boost pressure down to the 17psi, and leave it there unless otherwise needed. This would result in no performance gained despite improving the airflow of the engine, and this is essentially what the Learndown Feature does. There are other tables that come into play within the tune to contribute to the calculation of current versus allowed power output, but these are some of the basics.

Additionally, the stock tune and even the GM Stage 1 tune are designed to dramatically reduce the airflow output of the stock turbocharger at RPMs in excess of 5,000 or so RPMs. Above this rpm range the ECU will reduce the amount of allowed airload and the maximum amount of allowed boost pressure. The RPM-Motorsports Stage 1 and Stage 2 tunes raise these restrictions to a much more desirable level that results in increased power output to the wheels and a freer flowing engine.