What % of rated HP you can run an engine at is dependent on what type of diesel engine you are running. The old style turbo diesels need to run at "high" rpm for a certain % of their running time to blow out or burn off any carbon build up/glazing that happens when running them at the slower rpms one might run to achieve efficiency. However the new common rail and electronic diesels do not need to be run up and can run at extended periods at a reduced rpm. If you want the duel hp option then you would need the new diesels. --------------------------------- Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now.