Short version, “It takes a High School diploma to fix what a College degree broke”. or words to that effect.
BTW, it is recommended to lift the engine on just about any Subaru to change the plugs.
The lower voltage is only when the computer detects that the battery is fully or nearly fully charged. If the battery is low, it will charge at a higher voltage, also if there is a heavier electrical load such as HVAC fan on high and headlights on, etc.
The reason it does this is not so much for CAFE (corporate average fuel economy) but to extend the life of the battery. Todays cars are much harder on batteries that they were years (decades) ago. All modern vehicles do this now.
Basically the only real difference in plugs are what they are made of to last longer. A more expensive one made to your vehicle’s specs won’t make a bigger “BANG”. It will just last longer.
DON’T use “gimmicky” plugs that you see on TV. Use what your manual shows. Many of the “gimmicky” plugs can foul and may actually not provide the proper spark. If a better plug could be created, it would already be in your vehicle when you buy it.
Most plugs these days last for close to or as long as you own the vehicle. As long as proper maintenance is done, todays plugs will most likely outlive the vehicle.
Need more power? There are different exhaust systems, profomance chips, air induction systems… Consult your dealership for the brand you have or a reputable proformance shop. Certain alterations can effect your warranty too.
