Reflash! Ah-aaaah! Savior of the universe! Reflashing your car's computer merely changes its programming regarding timing, fuel-air mixture and other horsepower-upping inputs. The benefit of a reflash, besides the added power, is that it can be undone if you need warranty work done or have to have your car inspected by the state environmental department. The downside is that it really only works if your car is turbocharged or supercharged; reflashing a normally aspirated engine will only get you an extra half a horsepower, Zurschmeide says. And as with some of the others on this list, it only nets a big power boost if the factory programming is the limiting factor for your engine. Swapping out the stock computer for an entirely new module could help -- but that, Zurschmeide says, "has a very high price of entry."