i used the same scale i measure anything on. the front inner bumper is steal with styrofoam on it and same with the rear. they added up to just under a hundred pounds. and think about it, how much does a little fire extinguisher weigh compared to all that crap behind the dash? i also eliminated the front sway bar, rear dampner, inner fenders, air bags but reinstalled the covers, everything in the trunk and did the normal k-member stuff. cant remember everything, but if i didnt need it to go fast and it didnt change the look of the car, it was gone. but the inner bumpers is a must if your serious about shedding weight.
More weight loss ideas:
Take out side door bars if your car does not see the street. Remove heater/ac/radio. Take out inner wheel wells (front), take off wipers, wiper motor, washer fluid/pump, smog equipment. These are really more race car things.