The Toyota ZZ engine family is a straight-4 piston engine series. The ZZ series uses a die-cast aluminum engine block with thin press-fit cast iron cylinder liners, and aluminum DOHC 4-valve cylinder heads. The camshafts are chain-driven. The two 1.8 L members of the family, the 1ZZ and 2ZZ, use different bore and stroke. The former was optimized for economy, with torque emphasized in lower revolutions per minute operating range, while the latter is a "square" design optimized for high-RPM torque, yielding higher peak power. The ZZ family replaced the extremely popular cast-iron block "4A" engines.