A couple of blokes from my site used to race these.
50+hp worth of methanol burning formula500 engine into a Deltek rock hopper.
http://i156.photobucket.com/albums/t...ck20hopper.jpg
Honda Z50 with a YZ80 engine before Willowbank banned him from racing it.
http://i156.photobucket.com/albums/t...O/Hammer50.jpg