The SR block also sold as a heavy duty racing block. It appeared in 1970 in time for the 1971 Trans-Am racing season, and was used in the factory Trans-Am backed cars prepared by TRACO for Penske Racing, with Mark Donohue the primary driver. Since it was a standard factory part it did not have to be homologated under T/A rules, and "was not" used in the 2501 "Mark Donohue" Javelins built to homologate the "duck tail" spoiler. Those received standard 360 or 390 engines, buyers choice.