What is it?
Subaru’s third-generation flat-four engine makes its debut in this 2011 Forester, the boxer motor benefitting from a sump-up rework principally focused on reducing emissions, and improving economy.
Increasing its torque output has been the key, a goal that has induced a total redesign to accommodate a longer, torque-promoting piston stoke within the same dimensions as the previous engine.
Preserving the motor’s size has been no small challenge, Subaru aiming to increase the cylinders’ stroke without making it any wider, which would force costly changes to its cars’ body structures. Reducing the size of the heads has forced narrower valve angles, but the smaller combustion area resulting produces a more efficient burn, aided by variable valve timing.
Internal friction has been reduced by 28 per cent, these mods producing the same 148bhp, 10 percent better economy and a fractional increase in peak torque, which still occurs at a high 4200rpm. Good news for longevity is the switch from toothed-belt to chain-driven timing gear.