Sorry there, I was indeed referring to cubic inches rather than cubic centimeters. Hope d3mon cleared up the confusion for you. Either way, all the engines I listed should fit your Hpi Savage.
Any .21- .32 nitro engine with a pullstart/rotostart should fit. Unfortunately, options are limited in the pullstart/rotostart engines that are still available, as the heyday of monster trucks has long passed. Some options still available are dynamite .28 big red, .21-.28 SH branded engines with...