Jim, these heads originally were intended to be race heads, so most of the development and useage of them has been in that arena. The Duggan head, which is what my heads and Sissell's were originally derived from, have been used successfully in street engines, but still, due to the cost of them, historically most guys have used them strictly for racing.
The 150 HP gain was taken from an Inliner that upgraded from a race prepped cast iron lump head to a 12 Port head, and that was the gain he saw from the upgrade. So that just shows the potential of this head design, and like other manufacturers will say "Your results may vary". But a huge gain can be expected regardless of the HP level you are currently at.
One of many benefits with the 12 Port head vs. the cast iron lump head is that it yields a much higher flow rate at a lot lower valve lift. This is a plus because it allows the engine to make more power at a lower RPM as well because you can use a milder cam profile. Cotton's best lump head flowed 348 CFM, but it took .980 valve lift to get it, the 12 Port head can flow 340 CFM relatively easy at only .750 valve lift.
Since my heads are starting off as a raw casting, you have endless possibilities for valve size and porting packages, however, I think that a 2.02" intake valve would be the minimum you would be able to use. I also am considering making interchangeable casting cores for the intake ports. This will allow a head to be cast with a particular target volume more precisely, and eliminate a lot of time in trying to equalize each port, sorta' like having it cast in a ported configuration to begin with. Then have different cores to cast the head to tailor the customers needs, saving a lot of time in finishing the head as well.
The car in my avatar is my test car, so once I can test a few engine combos I can more accurately evaluate and give better guidance for engine builds.
As for the gains to expect from a milder engine using one of these heads, I don't know, but there are several on here that have also upgraded from a lump head to a 12 Port, so they might be able to give some feedback...I doubt they would go back to a lump head after using one though!
