These engines are actually not extremely expensive...think hobby money, like RC car type $. I did a bunch of research on them a while ago. Just like a real motor, you can make mods to them and everything. There are roots blowers kits with real working rotors, tiny little con-rods and pistons, you can buy stroker cranks for them and everything. Different cams produce different lopes. I'll see if I can find the website for the place in stockton. They are only like 20 minutes from my house...
Here's a good picture - check out the detail
Website
EDIT: link works now...I'm an idiot