basically its a piggy-back fuel management system, which corrects the richness or leanness of the fuel. usually with mods, exhaust, inlet manifold & i.k.etc your car will be running very lean, this can be dangerous & can f++k your car! the smt6 and a good mapper with a air flow meter (andy) can sort this out!!!+ gain a few bhp & a nicer torque curve in the process!