forged bottom end means the rotating assembly. rod and pistons r forged steel, and the pistons r forged aluminum. There r different grades of forged steel - 5140, 4140, 4340. 4340 is the strongest and is good to 1000fwhp if it's a scat, eagle or Probe piece. The pistons r forged aluminum and r usually notched for a ford inline head valve or a TW head valve.