The Magnum SOHC version, code ECH, develops 150 hp (110 kW) SAE (111 kW) at 6500 rpm, and 135 lb·ft (184 N·m) of torque at 4800 rpm. Chief differences between this version and the A588 include a cast aluminum SOHC cylinder head that more easily passes exhaust gases than the base engine, a camshaft that is optimized for higher engine rpm's, a factory welded exhaust short-tube header in lieu of a cast exhaust manifold, and a two-piece intake manifold. This manifold features unequal-length intake runners that are switched during engine operation by an electric actuator that controls butterfly-type valves in the shorter intake runners. The longer runners are always open, and provide a mild supercharging effect due to their length between 3000 rpm and 4800 rpm. The shorter runners, open from 4800 rpm to redline at wide-open throttle, also provide a tuned resonance effect due to their length. The shorter runners are also opened at wide-open throttle below 3000 rpm to provide an intake path to each cylinder that is as free-flowing as possible.[WIKI]
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