Additionally, many of the American cars provide better, or the only, horsepower improvement using the N/A option. I do not know of a database that lists cars by aspiration/power output and one quick way to tell is, after purchasing the car, you can go to the tune area of it's dealer and notice if the purple "turbo" box is darkened. I realize this is small help for someone playing through the game and trying to decide on an investment, but generally the larger engined cars, among them the TVR's, the NSX's and some Lotuses, are better suited by their very nature to N/A performance options and the game reflects this.