I havent personally used one yet, but I plan to. They are only made for the v6 as far as I know. But basically it changes most of the parts inside the engine (crankshaft,rods,pistons,etc.) essentially increases the displacement of the engine, to something similar to a larger engine, without actually changing any external component of the engine. so you get the power of a bigger engine while maintaining the balance of your Fiero. Like if you were to Swap the engine with a V8 or even a larger V6 the weight balance would be thrown off and that would decrease handling fuel economy and all kinds of other stuff.