Borrowing the technology from Honda's high-performance S2000 sports car, the IMA engine uses special compact, high-strength, forged-steel, carburized connecting rods. Carburization toughens the rod's surface so that it resists crack formation. Carburizing allowed Honda engineers to reduce the cross section of the connecting rods, thereby reducing their weight (always a penalty in a reciprocating engine) by 25 percent, while increasing their strength by more than 50 percent.
In the interest of friction reduction, Honda engineers specified a new lightweight aluminum-alloy piston design for the IMA engine. The pistons have a minimal skirt area and the surface of the skirt has been shot-peened. Shot-peening is a process in which a metal part, such as a piston or connecting rod, is blasted with shot-like particles, creating uniform, microscopic dimples on the surface. This dimpled surface is better able to retain a lubricating oil film. Shot-peening the IMA engine's pistons accounts for another 1.5- to 2.0-percent reduction in internal friction.
The Insight IMA engine features a magnesium-alloy oil pan. Like a cast-aluminum pan, the Insight's magnesium pan adds stiffness to the engine block, helps muffle engine noise and also helps to cool engine oil, but it is 35 percent lighter than aluminum. The magnesium alloy specified for the Insight engine's oil pan is a new type that exhibits less thermal-induced expansion and contraction (creep) at high temperatures, so the oil pan remains oil tight.
Honda engineers designed additional weight-saving measures into the Insight's magnesium oil pan by incorporating the engine oil-filter bracket, AC-compressor bracket and an engine-block stiffener into the casting.