Actually, the new Hemi engines aren't truly hemispherical. They are somewhat more hemispherical than most engines, but their design really isn't anything revolutionary, nor is it true to the original Hemi. It's somewhat of a hybrid. The reason why they are not as true of a Hemi as the original is because while the design creates a lot of power via the ability to flow huge amounts of fuel and air and the plug location as others have mentioned, it's incredibly inefficient. That's the reason why they were dropped in the early 70's in the first place, is because they were impossible to get past emissions. So they had to somewhat compromise between power and emissions/fuel mileage (another thing the originals were horrible with) in order to be certified. That's why they have the cylinder deactivation, because it's an easy way to get the emissions just low enough for the government to pass them. They market it as helping with fuel mileage, but in reality it only works much on the highway in cruise, and even then it only has a 2 or 3 mpg advantage over the full 8 cylinders. If I could find a schematic of the engine I could show you, but I've seen it from a "build" a car magazine did.