by nearly 500 additional units (UP 3999 and below, UP 5000 and above, except for 3985, which was left vacant for Challenger 3985). This locomotive model is also built for export, and is still catalogued by EMD (at ). CVG Ferrominera Orinoco has 6 SD70Ms that were built as an add-on order to UPs FIRE cab equipped SD70Ms. Companhia Vale do Rio Doce (CVRD) in Brazil has ordered 55 of this model for service in Carajas pulling trainloads of iron ore. Since CVRD track is gauged at , a wider bogie, the HTSC2, was designed for these units by EMD. SD70I (1995) The SD70I is a version of the SD70 which has been fitted with a cab that is isolated from the frame of the locomotive with rubber gaskets (officially known as a "WhisperCab"). The isolation reduces noise and vibration from the prime mover. A seam is visible across the nose and on the long hood where the cab connects with the body. 26 examples of this model locomotive were produced, all for Canadian National. The WhisperCab feature was incorporated into some SD70MACs and was standard on both the SD80MAC and SD90/43MAC models. SD70MAC (1993-2004) The SD70MAC uses three phase AC traction motors. Production of the model commenced in 1993, competing against the GE Dash 9-44CW. The majority of SD70MAC models were produced with the EMD 710 prime mover while later units are rated at and feature EMD SD45-style flared radiators. The Alaska Railroad ordered their locomotives with head-end power to make them suitable for both freight and passenger service; no other railroad ordered this variant. The trucks were replaced with HTCR-4, instead of HTCR-I on former model. The SD70MAC is no longer produced due to EPA regulations, and was replaced by the SD70ACe in 2004. In total, 1,109 SD70MACs were produced, purchased by Burlington Northern (and its successor, BNSF), Conrail, CSX, Transportación Ferroviaria Mexicana (TFM; units now owned by Kansas City Southern Railway (KCS)), and the Alaska Railroad. SD70ACe (2004-present) The SD70ACe is the successor to the SD70MAC with design changes to comply with emission standards. The engine fires with 15% lower internal pressure to improve emissions and features fewer internal components in the inverter. The SD70ACe is equipped with EMD's 16-710-G3C-T2 prime mover, rated at ; later Tier 3 models are rated at , and have a thermal efficiency of almost 36%. They are rated at continuous tractive