After going through each car and upgrading the engine to its maximum horsepower (including available conversions), this is the list I came up with that produce over 900 hp:
HP | Torque - - Engine name
1443 | 1267 Bugatti Veyron SS
1287 | 1112 SSC Ultimate Aero
1257 | 1082 Bugatti Veyron 16.4
1228 | 1015 Koenigsegg Agera
1200 | 1155 Hennessey Venom GT
1124 | 997 Viper GTS
1123 | 821 McLaren F1
1104 | 937 Pagani Zonda Cinque
1102 | 847 TVR Cebera Speed 10
1094 | 774 Ferrari Enzo
1084 | 918 Bentley Continental SS
1083 | 793 Maserati MC12 V12
1082 | 702 RUF RGT-8
1079 | 789 Ferrari FF
1076 | 711 Ferrari 599 GTO
1065 | 938 Dodge Viper '08
1059 | 731 Lambo Aventador
1052 | 721 Porsche Carrera GT
1050 | 693 Toyota Top Secret Supra
1050 | 912 Saleen S5S
1045 | 1015 Mercedes SL65 V12
1037 | 697 Nissan MINE’s R34
1031 | 1002 Dodge Viper CC
1023 | 665 Lambo Miura C
1016 | 867 Devon GTX
1012 | 905 RUF Rt 12 R
1006 | 727 Aston One-77 V12
1002 | 757 Nissan GT-R R34
995 | 833 Bertone Mantide
992 | 800 Spada Coda
982 | 840 Ford Shelby GT500 '07
980 | 816 Cadillac CTS-V '09
978 | 873 RUF Rt 12 S
976 | 833 Chevy ZR1
976 | 967 Pagani Huayra
972 | 801 Chevy Camaro ZL1
965 | 713 Ford #25 FG Falcon
964 | 714 Lambo Diablo GTR
957 | 837 Gumpert Apollo
956 | 678 Lambo Murc SV
954 | 680 Ford/Holden V8 Supercar
951 | 850 Ultima GTR
950 | 708 Aston DBS
946 | 697 Lambo Murc Unicorn
943 | 713 Mercedes SLS
943 | 653 BMW M6 2010
942 | 653 BMW M5 E60 2009
931 | 669 Lambo Reventon
929 | 843 Mosler
925 | 772 Ford Shelby GT500 '10
923 | 575 Ferrari FXX
919 | 723 Lambo Murcielago
918 | ??? Aston 1988 V600
917 | 564 Lexus LF-A
910 | 630 Wiesmann GT '10
907 | 800 Dodge Challenger 392
907 | 597 Ferrari 599XX
905 | 837 Saleen S7
905 | 633 Ferrari 599 GTB
899 | 708 Chevy/Ford Stock Car