[Technick]

Speed density works fine at wide open throttle on a modified engine, will run like crap at idle and part throttle. ALL hydraulic roller cams (excuse me, MOST) especially the alphabet cams (B,E, X,Z ect) and MOST aftermarket cams will nose over and be all done after 6,500 rpm. The reason is that these cams are designed for the "stock" 5.0 computer and valvetrain. The weight of the roller lifters themselves limit the amout of rpm that the engine will rev. If you get more valvespring pressure to offset the weight f the hyd. roller lifter, then you usuall collaspe the lifter from to much spring weight. Besides, the cam profile itself is all done just after 6,500 rpm. I once put solid roller lifters on a Hyd. roller cam in a carberated application trying to get more rpm's out of the cam by going to the much lighter solid roller lifters and ethe engine stilll nosed over after 6,500 rpm. Just not enough duration, the lobe seperation angle is for computer cars not carbs, ect. ect.