ok, im kinda new to this whole thing , I was wondering when people talk about their bottom end being built, what does that refer to, and why would someone need to build their bottom end???

 

The "bottom end" is anything below the heads. This includes the engine block,pistons,rods, and crankshaft. Also all the support system, like main bearings, etc. A "built" bottom end usually refers to a forged, instead of cast steel, pistons, rods, and sometimes crankshaft. These parts are much stronger, and obviously able to handle greater stresses than their cast counterparts. This is a bit of oversimplification, but gives you the general idea.

 

http://auto.howstuffworks.com/camshaft5.htm