[Jay1823]

From the looks of the setup these aren't even true superchargers. They look like turbo compressor housing with modified turbine shafts. Which would easily explain the horribly low psi #'s and that tiny pulley. There trying to increase there rpms as much as possible to make any psi at all out of that turbo compressor. Pretty dumb though since turbo compressor wheels spin at over 100k to deliver there boost. I doubt this thing even hits 10k, it's barely pushing any air.
Livewires correct about that hp # too. Usually you can say 1 psi of boost generally equals 10 hp in a tuned engine, + or - of course. But when your starting with an 18 hp engine 3-4 psi isn't even going to come near 42 hp, maybe 25-30 but no way in hell is it 42.
If you want ideas i can tell you how to put together a turbo system using a bunch of stock parts that will be reliable, cost around 500-750 dollars and produce WAY more power than that thing.