Originally Posted by haen
No, I don't care about HP/liter and neither should you. It's not like there are engine displacement restrictions for production cars.
Basically incorrect here. There are very heavy taxes in many EU countries based on displacement alone. Hence why many cars are infinitesimally lower in displacement than a rounded number in liters (specifically M3 = 3.999 l, taxes for 4.0 l and above). The reason you should care about hp/l is not for the performance it gives you in your car but because it is a challenge of extremely difficult engineering. It is simply doing more with less which is univerally valued in just about any endevour. In competitive auto racing where you have a displacement limit this is obviously the key to a great engine at a given displacement.