Teka grounding kit ba ang tinatanong mo sir?
Kung grounding kit sa bagong car, walang effect yan, posibling magkaroon lang ng ground loop ang sasakyan mo sa daming ground wire na umiikot ikot sa loob, can also possibly cause a noise interference and hum to your audio.
Ganoon din sa old cars kung lagay ka ng lagay ng ground kahit saan sa loob ng car.
Good grounding kit for old cars can restored it upto 80% to 90% or possibly higher engine performance.
Kung VS naman na naka-market, New car and old, no effect at all, IMHO.
Just like what sir yapoy86 says, 1 FARAD or 3 FARAD BIG BULKY CAPACITOR is much much better than marketed VS.
1 FARAD like this:

or this one:

White Cap is worth 14,000 pesos for 1 FARAD only.
That's damned OVERKILL using it without HIGH Wattage Audio setup.
