For the items making up the extra weight of the 718 v 981, see below this GT4 comparison from Sport Auto.
Generation Differences:
Exhaust system inc GPF + 10.8kg Engine inc stop/start + 7.7kg Diffuser/undertray + 6.5kg Other trim + 3.2kg
Specific Differences of the GT4 Test Vehicles
718 had Clubsport option + 19.9kg 718 had racing bucket seat + 9.0kg AGM battery v 981 LiFePO4 + 16.1kg
Also and separately to the individual vehicles above, the rules for published manufacturer weights changed between 981 and 718. On the former, lightest possible configurations were published, so Aircon delete, PCCBs etc. On the latter, typical configuration weight had to be quoted, this rule change adding at least 50kg to post-change published vehicle weights.
Generation Differences:
Exhaust system inc GPF + 10.8kg Engine inc stop/start + 7.7kg Diffuser/undertray + 6.5kg Other trim + 3.2kg
Specific Differences of the GT4 Test Vehicles
718 had Clubsport option + 19.9kg 718 had racing bucket seat + 9.0kg AGM battery v 981 LiFePO4 + 16.1kg
Also and separately to the individual vehicles above, the rules for published manufacturer weights changed between 981 and 718. On the former, lightest possible configurations were published, so Aircon delete, PCCBs etc. On the latter, typical configuration weight had to be quoted, this rule change adding at least 50kg to post-change published vehicle weights.