 Power output of the turbocharged SD24 was 33 percent higher than the of the concurrent Roots blower-equipped SD18s with the same engine displacement, per axle, but the power output of the turbocharged GP20 was only 11 percent higher than the of the concurrent Roots blower-equipped GP18s with the same engine displacement per axle, due to the limitations of the traction motors then available.Nevertheless, the turbocharged GP20 provided full rated power at all altitudes, which the Roots-blown GP18 could not provide.The turbocharger was the then-new EMD mechanically assisted turbo-compressor.