SEI MARINE PRODUCTS - SE206 2.0 Gear Ratio 25" Driveshaft Our SE206 Lower Unit is a replacement for Mercury 2.0, 2.4, and 2.5 Liter V6 Engines. SE206 Lower Units are not designed to replace Sport Master, Torque Master, CLE or other high performance gearcases. The SE206 Lower Units have a 4 3/4" bullet diameter.