darkSpyro

Besides unlocking parts, what does it do otherwise? Does it boost anything in a race or story mode? Also, when i supercharge a vehicle, then switch characters real quick it stays supercharged.

Makes vehicle have stronger attacks as well as boosting the driver's health and power.
If you take out the signature driver then your vehicle won't be supercharged anymore but retains the supercharged parts

You have a power boost both in the Skylander and the vehicle, in Story and Race. You can't make a vehicle stay SuperCharged with another Skylander, but I think that you can use the SuperCharged mods in racing with any Skylander (I remember of a video where Nightfall is with the SuperCharged mod set in Stealth Stinger).

ah, thanks for the quick answers. how much of a boost does it give?

Depends on the vehicle/Skylander. Each mod changes different stats, and the rule is the same in the SuperCharged mods. You can check the vehicle mods and see the differences. For the Skylander, I don't know if there's a pattern, but it works just like Elemental Power.