hmmm, i'd only push 6 to 7 on a stock d series bottom end...that and any more boost and you'll need a few more extras like fuel supply and decent spark. i'd go 6 and then once in a while 7 or 8, just to be safe...it's hard to tell you exactly how much boost to run safely. who's to say one of the rods are kinda on its last leg and ready to give if pushed too much boost? i'd go 6 and it woud be safe, give you a significant hp and tq increase..you can always go and get some eagle rods and put em in. they are pretty cheap and if you know what you're doing you can put them in yourself.