I saw an ad in the Power Manual of one of their 12 port heads that said it was a 60 hp bolt on.
That would be a conservative estimate. There have been several to experience over 100 HP gains with more aggressive engine combos over a lump head. It is a sizable upgrade in cost, since you have to have specific add-ons to also go along with the head that cost extra above just the cost of the head unfortunately.
