Thunder Max Touring® Models (w/o Center Cool Motor) 2021+

ThunderMax is a performance-driven, award-winning ECM built exclusively for EFI-equipped Harley-Davidson® motorcycles. Designed as a stand-alone replacement for the factory ECM, the 309-591 arrives fully assembled with wide-band oxygen sensors, plug-in harness, AutoTune module, USB communication cable, and everything you need for a straightforward install—no wire-cutting, splicing, or dyno required.
 
At its core, ThunderMax uses proprietary AutoTune technology and a closed-loop control system to continuously read, adjust, and perfect your air/fuel ratio in real time. With fueling points mapped every 1.5° of throttle and every 256 RPM, the system delivers unmatched precision for smooth, consistent performance in all riding conditions. A built-in barometric sensor accounts for altitude and ambient air changes automatically—just load the map that matches your build and ride.
The ThunderMax 309-591 also features knock correction for timing adjustment, adding another layer of performance by adapting ignition timing on the fly. And unlike other aftermarket tuners, ThunderMax fully supports factory functions, so you don’t lose the stock conveniences your Harley came with.
 
Riders get complete flexibility: run a basemap and let AutoTune handle the rest, or dive into the ThunderMax software—free to download from our website—to fine-tune AFR maps, ignition timing, startup fuel, idle speed, rev limits, and speedometer calibration. The system also offers robust data collection and diagnostic capabilities, letting you log, monitor, and analyze critical engine metrics for deeper insight into performance.
 
The result? Sharper throttle response, stronger rideability, and that deep, tuned exhaust note that makes the bike yours. Compatible with high-performance cams, turbo, nitrous, and supercharger applications, ThunderMax 309-591 is engineered, built, and supported in the USA.
Notice: ThunderMax ECMs utilize 18mm O₂ sensors. Factory exhaust systems are equipped with 12mm ports; however, nearly all aftermarket exhaust systems are manufactured with 18mm ports. If using a factory exhaust, you may weld in 18mm bungs. Bungs are not included.