Originally Posted by
LOSIRACER77
Anyone have an answer for this question??
The biggest differences between the two kits are the plastics used and the shocks. The B4.1 uses more flexible plastic than the carbon composite in the B4 FT kit. Also, the B4.1 has new V2 shocks which do away with the clip and spacer setup for the O rings in favor of a bottom loading cap for keeping the seals in place.
More detailed info can be found
here