I came across this engine on Ebay.
It says it is a HP3 8.1 that produces 525hp.
Googling it I came up with a few articles about 2002/03 and that it was used in boat racing.
Apparently a HP1 is a 375hp, a HP2 is a 425hp and this HP3 is a 525hp. They are all based on the Vortech 8.1 or 496.
They then seemed to have disappeared.
Does anyone know anything about it especially the differences between a 425hp and this one?