When cars were first required to have catalytic converters, manufacturers rushed to slap them into place. They didn't do one's performance any favors, though they did help the air we breathe some. It took decades for catalysts to improve, with even cars from the 1980s and 1990s getting gummed up in the converters. And if you added leaded gas to that equation? Well, you were lucky if you could make it up a hill. Try this: Swap an old catalyst out for a modern aftermarket high-flow number and feel the difference in the pedal. Do this along with a cat-back exhaust, Zurschmeide says, for the biggest bang for your buck. He also notes that it's illegal to remove a catalyst that's not broken -- and there are some hefty fines for punishment. Do not, under any circumstances, knock a hole into your catalytic converter with a wrench you happen to be holding, requiring it to be replaced, perhaps by a high-flow catalyst. You hear that? Do not knock a hole in it.