The problem with hydraulic cams is finding the corect valvespring. plus the lifters are sooooo heavy. Those 2 things keep them from making it to 6500 RPM.too much spring pressure and they bleed off too fast. I sold that 427, and am building a new 468 this one has a custom solid roller on a 112 LC. Again i did that because of the nitrous. i am looking to run this motor to 7000 RPM on th nitrous.