For the GC/GM Impreza WRX, the EJ20G engine had a water-cooled, Mitsubishi TD05 turbocharger; the rotational speed of the turbine ranged from approximately 20,000 rpm to 150,000 rpm and peak boost is understood to be around 11 to 12 psi. To prevent excessive boost pressure, which could cause knocking and heavier thermal loads on the pistons, the EJ20G …