I went to the 605, why not go as big as you can. Mine is head limited but still makes 853hp@5782rpm and 818ftlbs@4818rpm. It's a monster down low to the shift point.513hp and 764ftlbs@3500 rpm. It hold 800+ftlbs from 4100 to 5500rpm. It runs on 89.5 octane and never needs to see more than 6500rpm.Dave