Z6,Trust me Ive blown three D15s, With stock internals and at 10 pounds. The true Power is out of a z6. Do not build a d15b7 your wasting time, Not enough trq, or power. If you want 250-300hp. Suggest the z6,with aY8 tranny. I made 208hp, and 190 trq on d15 b7. But not safely... Do not make the same mistake that I did. Not unless you just like to blow things up.