58mm of Bliss
I havent read the whole tread, so perhaps you have done some of this already.
Get rid of the electric window openers, lot of weight. Replace windows to lexan ones. Airbags in doors have to go too, replace the doorpanels with a single cheet of CF. Ad a strap to close the doors with. I'm not sure but i think leather seats are heavier than fabric ones, replace and make sure they are manually operated. Or get proper racing seats, CF ofcourse, replace backseat with two racing seats also.
On the outside, as mentioned before CF hood, trunk & roof. Front fenders perhaps if available. I have seen CF doors for the Ci model. CF rear and front bumber. Lighter wheels is a good thing, makes more difference than you would belive.
The fueltank is a heavy beast, replace with a fuelcell in trunk. At the same time get rid of the carpet in the trunk. Original exhaust system is built to last a long time. Heavy!! Replace with a lightweight system.
A set of coilover chocks will probably save some weight too.
Quite expensive, but if it should make any difference at all you have to go all the way. I would rather begin in the other end and gain more power from the engine with a supercharger. And still have a sporty car with comfort.
Will continue following your progress with interrest.
Since I have a little bit of experience with everything you suggested:
-Using Lexan to replace any window makes a vehicle non-street legal. In case you were to do this (illegally) your weight savings would be under 10Lbs for both sides.
-The inner door panels weight 13 Lbs each.
-Airbags are a total of 13 Lbs for 5 of the front 6. (You want to keep the steering wheel one for looks) If you are going to remove one, you may as well removed them all because the system will be disabled at that point.
- Stock seats are 65lbs, aftermarket fiberglass ones with brackets are about 30 Lbs. CF seats will save you a whopping 4 lbs over fiberglass for 3-4 times the price.
- Stock fenders are 8 lbs...hard to make them lighter than that without some structural issues.
- Hood, trunk, roof, and doors will cost 6k for about 150lb reduction. To do the doors you will NEED a roll cage with either an X brace or nascar style bars. (Again, part of the road specs for cars to be street legal) The cage will add all of that 150lbs savings back into the car if done right. Don't do the doors, and you'll save about 40- 50 Lbs total for around 4+k.
-Wheels you can go about 16lbs lighter than stock total before it gets to be either really expensive or really unsafe. IMO though, the best mod of the bunch. Affects acceleration, braking, and handling a great deal. I added some larger wheels that were 20lbs heavier than stock total and lost about 2 MPH at the drag strip. (Call it a 20hp handicap at the traps)
-The fuel tank is made of plastic, and it's lighter than you think. The only reason why fuel cells weight less than the stock tank is because they are smaller and don't have all the emissions stuff attached to them. Remove the emissions stuff....and you guessed it...you're not gonna be street legal. Also, the mounting of the fuel cell will add some weight, as you are required to have a certain gauge of material around it and it will need supports.
-The carpet in the trunk weights 8 Lbs I think. Think big back there...like a spare tire and you'll hit the jackpot!
-The stock exhaust system is 69 Lbs. The TSE3 weights about 60lbs unmodified, 65Lbs with cats installed. Spend big bucks on a Kromer Kraft custom exhaust with Aluminum center sections and you will get down to a feather-like 40Lbs.
-Coilovers are an average of 10Lbs lighter than stock.
Buy a supercharger and you'll go faster than with all the above done for 1/4 the price and still have a car you can give chicks a ride in.
(From the PEI330Ci BMW weight archives)