What contributed to the 200 lb difference between a stock 71 and the 72?

thanks in advance

everything ive ever seen says that in the later 240z's Datsun used slightly thicker metal to make the unibody part of the car.

I have a 72 240z and have inspected my unibody/frame rails etc. I compared my underbody metal thickness to an early 71 240z, It seems that unless its was my imagination or my micrometer has an error, the newer 240s seem to average one mm thicker in several key areas of the unibody supporting underbody structures. I can get exact mills, but i lost my sheet. dang. Anyhooo, seems the newer z's have better metal

my stock 5/71 240Z with all the trimmings including spare tire weighed in at 2320.

now my 7/72 240Z weighed in at 2300 even. no spare tire. no bumpers msa aero kit all the way around.

there is extra weight in there. just not to much