I want to understand how Honda calculates the combined horsepower ratings for i-MMD two-motor hybrid systems. Specifically, how the Clarity Plug-In Hybrid can produce Honda's claim of 212 horsepower. Clarity forum member ab13 thankfully directed us to the very interesting 2013 paper authored by Honda engineers Naritomo Higuchi and Hiroo Shimada. It is titled "Efficiency Enhancement of a New Two-Motor Hybrid System." This paper describes three basic drive modes for Honda's i-MMD two-motor hybrid system (these are the authors' words): In "EV Drive", the traction motor physically connected to the driveshaft propels the vehicle by using electric energy stored in the battery. In "Hybrid Drive", the traction motor is driven by electric energy generated by the generator using engine output. The battery behaves as a passive device to provide lack of engine output or be charged by surplus energy. In "Engine Drive", the engine-drive clutch located between the engine and the wheels is engaged, and the vehicle is directly propelled by engine output. The paper's Figure 11 graphically depicts the operation of these modes. Of special note, the figure clarifies the operation of Engine Drive mode by showing that in this mode the traction motor switches to generate power to recharge the battery, as it does when the car is decelerating (assuming the battery is not already fully charged). Honda has stated that the traction motor produces a maximum of 121 horsepower in EV Drive mode (battery power only) and up to 181 horsepower in Hybrid Drive mode, when the starter motor/generator is functioning as an engine-driven generator to supplement the electric power coming from the battery. Honda specifies that the Clarity's 1.5-liter engine produces 103 horsepower. Has Honda made improvements to the i-MMD system since this paper was written to describe the 2013 Accord Hybrid? If not, how can the Clarity produce 212 horsepower? Figure 11 does not illustrate any mode where the engine and the battery-powered traction motor combine their outputs. How can the Clarity Plug-In Hybrid produce any greater than 181 horses to turn the gears that drive the front wheels? Furthermore, how is that the new Accord Hybrid, with its 181-horsepower motor and larger 2.0-liter, 143-horsepower engine also produces exactly 212 horsepower?