just remember these stock engines have iron heads & pistons way down the bores & worn bores ect ect. pinging is what kills engines & the alloy heads will help with that, as well as zero deck & quench, big ports & larger valves nice thick sleeves that are held in place by grout= hi cylinder presure, so mine will hold the presure rather than blowing by the rings. one of the books i was reading said turbo motors respond to all the things that a NA motors like, just the gains are more noticeable. 383 / 400 engines, there not running efficently untill there well into the rev range, just like other over bore engines ie [Edited by Moparts - Family Friendly Site - Keep it clean] bikes & cars indy cars & F1 cars ect i think the sweet spot will be over 6000 rpm. i'll happerly take mine high 6000rpms as 7000ish is the cut off for the oil system.