I'm not sure why you need a voltage stabalizer on your car? Most all components already use a zener stabalizer if they need one!! The only critical component on most cars is the computer, and it is already regulated to +5v -5v and 12v, so using an other regulator will make no difference.The voltage from your alternator is also regulated to about 14v when it is charging properly and only under very high electrical loads, at low idle will your voltage drop to around 12v ,or your Battery needs to be replaced. I wouldn't waste my money on a stabalizer and would buy a good battery instead.
On Ebay I see there is a device called a Voltage Stabilizer put out by several manufacturers that claim having a stable voltage will actually improve performance. This is the first time I have seen something like this. Before I buy it I would like to hear from those that know if this is worth the money or not. Thanks