I do remember that old of the box with my R/C stuff, the SX LiPo weighed in at just under the legal minimum with a typical lipo.
I wanted ti to be just over the 1600g mark so as to make sure it doesn't get too critical on the scales for scrutineering.
I leave my roll bars fitted and just remove one link if they are not being used - so I guess that helps a little bit.
Either that or it must be the heavy shock oil that I was using
Stu was using the S1 car so maybe the S1 composite is also a bit heavier - he was really going well with it