[Beyond]

slow my car down?

[dollarbill]

The weight of it is the real issue. When you add weight to a car yes it slows down.

[LqDFx]

How much do you plan on using that you are worried about weight? I mean a 20 sq ft sheet of it should do your whole trunk and only add about 10 lbs. If you are that worried about weight, you should not even put in the extra speaker(s) and amp(s). I would say that I have added about 50-60 lbs to my car with just the two 10" subs and the box alone! Then add the extra for the 2 power amps at abotu 15 lbs each and you are talking close to 100 lbs. Ofcourse you can make up the extra weight by getting rid of your back seat!

[Beyond]

I've just heard the stuff is heavy. Will both doors covered and the rear deck make a big difference, or not much of any at all? Also will these areas covered (a) stop vibrations from these areas from the speakers? (entire rear deck, parts of doors) (b) make it impossible to hear exhaust/engine?

[LqDFx]

Dynomat is the same type of stuff used by car manufators to get that quite ride. They put thicker insulation in the doors, along the firewall, in the body panels, and the luggage area. If you are driving a Tauras you are not worried about weight.

Think of it this way, both doors and trunk you maybe adding like 60 lbs of Dynomat. You will stop some but not all the vibration, mostly you will not hear it. As it stops the sound from excaping, it also stops the sound from coming in!