[Dominik]

toivo,

there is no real one on one hp / weight equivalent, but 10% less weight gives you 10% more "hp", which you really feel only up to say 85 mph. Above that your car's weight is small in comparison to your car's aerodynamic drag. Especially when you go faster.

It's a lot different at breaking or cornering in case you are racing. Every pound saved you save by the square. So 6 lbs saved is not twice as good as 3 lbs, but a lot more.

I won't go more in to detail here, but i.e. Posche went to great lenghts reducing the 1992 RS weight to 2700 lbs compared to the 3200 lbs for the street model.

Still that 1992 RS is a winner in his field compared to the new equivalent, the GT3, due to the weight(and rear end ratio in this case)
Just to give you an idea.

Dominik