I would think it would be of most meaning if usable HP with a driver was used for a HP to weight ratio.
Get a 1/4 mile trap speed, correct to sea level for alike comparison to others and then use a racing calculator for a HP number. Divide HP into you and the car weight.
If car and driver is 2600 lbs and it traps 125 mph, which is about what 550 to 600 engine HP Cobras often seem to be, it would be about a 400 corrected rear wheel HP car.
6.5 lbs per 1 HP.
http://www.pro-system.com/calc.html
http://www.modulardepot.com/density.php