I didn't know the actual weight of the doors, but I was telling a friend that his Silvia door weigh about 4 times less than my door.
Since it's not registered for passengers in the back (hence no seatbelts) I think I might take the rear seats out. That might help a bit. Eventually down the track I guess I'd swap the seats for some light weight reclinable racing seats.
The D1 JZZ30 even has carbon fibre doors and bonnet to cut down on this rediculous number.
You obviously have an MZ20 race car? What type of racing do you compete in? Some pictures of your car, interior and engine bay would be great! What modifications have you made? I'd like to compete in circuit sprints and drift.