FastestLaps you should have all the data using the same units. Here is the problem: horsepower has multiple interpretations, please read http://en.wikipedia.org/wiki/Horsepower.
I suggest to have only kW in database and to publish something like this: 377 kW (505 HP SAE, 512 HP DIN). Or publish only kW.
Also the weight of the cars is a decisive parameter. Don't let marketing tricks fool you, use the "curb weight", not "dry-weight".
"Dry weight - Lamborghini continues to favor this utterly useless figure over true curb weight due to the marketing benefits". Please read http://news.windingroad.com/auto-news/lamborghini-lp640-murcielago-roadster-lands-in-la-and-poses-no-surprises/