Gordo

Tomcat,
Ok, you have my attention. I will be the first to admit that my experience with superchargers is somwehat limited. Back in the mid 90's I worked in the service department for a local marine dealer that installed "Prochargers". This period is where I gained my experience, (and my opinion), with centrifugal superchargers. I've seen a couple of other brands, (Vortec, Paxton), but don't really know much about their systems. At the same time the old Merc 525SC seemed to work pretty well.
Since then most everything has gone efi. If this were my case I would be looking at nothing but centrifugal superchargers. Alas, I'm still one of the old diehards with carburators. Besides, money is an issue, (isn't it always?), and since I already have the carbs and flame arrestor in a box ready to install, I thought the roots would be the less expensive way to go.
BUT, If you have a better mousetrap, I'm all ears.

tomcat

Gordo:

If there is a way to compare it might be by looking at $/HP gained.

If you started with an 500 HP engine and pumped it up to 650 HP with a Roots setup for $4000.00 that would be a good "investment" at $27/HP gained

On the other hand, if you paid "full retail" for an Rtech system plus $1300 for a modified carb and boost referenced fuel system you would have $8000.00 tied up in a supercharging system, but you would make 800 HP. Same $27/HP gained, same value for dollar in my book.

Now adding 500 HP for $500 bucks would be great but I can't seem to design one of those; something about the laws of physics.

As I said above, just get supercharged, we'll convert you later...