For the purpose of HTS, Hp or Kw ratings aren't relevant for diesel engines that are used for propulsion of road vehicles. If it's a marine engine, or a stationary motor (generator, industrial motor, etc.), then yes, HP matters and there are different codes for different ranges of power.
Both the 1HZ and the 1HDt are diesel engines that are used for the propulsion of vehicles that would be under HTS heading 8703 or 8704, depending on whether the vehicle is passenger carrying or cargo carrying by nature.
Pretty sure 8408.20.20.00 is what you're looking for, but your Customs Broker would know for sure.