I have the one that Steve Segal mentioned and have been racing with it for three years. It has eliminated the problem of burning up the power steering pumps and does run the accessories slower. I did not do a horsepower check, so can't add anything here. I doubt that it adds any power, but it does seem to help reduce the strain on the alternator, p/s pump and water pump when running near red line, as you often do in racing. I have seen no problems with idle speed battery charging.