A lighter car means your cars engine doesn’t work as hard during acceleration which increases acceleration speed as well as economy. The things listed below are all things I have done to my own cars, however check with your country / states laws to make sure they are legitimate modifications before attempting.
First of all, it all depends on how much you are willing to sacrifice in terms of comfort to make your car lighter.
First check these things:
Keep your tyre pressures even and firm at all times, do regular services and oil changes too. These will help the car run smoother and cost you less fuel and repair bills of a poorly maintained car.
Basic D.I.Y things that cost little or no money:
1) Remove the back seats
2) Removal of dash trimmings, door cards, stereo unit, carpet, sound deadening under carpet, headlining, sound deadening and insulation in roof ( located behind headlining, not all cars have it )
N.B: if you want to lose weight but don’t want to ditch the carpet you can always pull out the sound deadening and put carpet back.
3) Removing all inside door components – window winders, sub framing etc.
4) Removal of spare wheel, jack, tools etc – do at your own risk, i did because i am a member of AA roadside insurance, who provide all this.
5) Scraping off all under seal from car, ( this is usually very thick and heavy and not needed ), replace with brush-on under seal bought at any place like Super cheap auto or Repco. Much lighter, paint-like substance that does the same job.
6) Remove air conditioning and airconditioning lines/ filter etc
7) Some hatch-backs and cars with gas struts in the boot will have lead weights located inside them or on them, these can be removed.
Gearbox ballast, located on sides of most rwd cars, some say it helps prevent vibration, i removed and have no issues
9) Removal of window washer bottles
From here it can start to cost money, but here is where the it gets noticeable.
1) fibreglass guards / bumpers, bonnet, or carbon fibre
2) Perspec windows
3) Dash removal and replacement with plastic
4) Light weight alloy wheels