All AMXs came with four-barrel carbureted small block[36] AMC V8 engines in several versions: 290 cu in (4.8 L) (225 hp (168 kW), N-code), 343 cu in (5.6 L) (290 hp (220 kW), T-code), as well as the 390 cu in (6.4 L) "AMX" featuring 315 hp (235 kW) with 425 pound force-feet (576 N⋅m) of torque (X-code). All derived from the same external sized block. However, the three engines differed vastly internally, with the smallest engine having small intake and exhaust valves, thin block webbing, and a cast nodular iron crankshaft; the 343 used larger valves with a thicker block webbing; and the 390 moved up to a forged steel crankshaft and connecting rods, as well as larger rod bearings, 2.250 in (57.15 mm) compared to 2.090 in (53.09 mm) in the smaller two versions.[37]