To add to what Jeffc said... if the car's were equal hp/weight, the lower weight car wins. There may be too much focus on the hp/weight thing...which matters more in straight line acceleration.
Lower weight means you can take corners faster (less mass pulling sideways. Lower weight means you can brake deeper (less mass to slow down).
And the advantages of a midengined design for racing has already been gone over on the forum. So it won't take much in terms of hp to keep up with the higher powered cars.
For an example at this morning's race. I was in a Toyota MR2 Spyder. In my run group were a couple of race prepped Vipers (running in ASP) and Z-06 Corvettes and also some other odd racing cars. All of Super Stock and ASP. All in all, maybe 50 cars. I beat them all with my 140hp Spyder. Set Top Time of Day until a race prepped new Evo came out and beat me.
Now, I am going off to race tonight at Irwindale in my 42hp shifter kart. It weighs 200 pounds, but more importantly, the braking zone is incredibly small and it sticks like a limpet while turning.
What is my point???

Don't worry too much about horsepower. It's only one part of the car and not the most important part. Weight is more important. Driver skill is also. Unless you are into dragracing...in which case this is not the right car.