David, if I recall correctly, the 5 hp gain was with the modified Prince head in place of a stock head? It would be nice to know how the unaltered Prince head would have done.
The D shaped ports are said to work very well on LS 9 Corvette engines, tho like the Prince heads, the actual exhaust port appears smallish compared to expectations.
Glen
Glen,
Yes, you are correct that it is not a perfect test. It is also a 500 cc head. I think it is worth pointing out that the Terry Prince heads are basically "big port" heads, except Terry's heads did not change the valve angle. The second item to note is that Terry and John built the heads for the street. They were designed to make gobs of torque, but not top end. Terry and Mal have modified their bikes at least somewhat to do the land speed racing.
For max power you really need revs. In road racing you can compromise a little more as torque to get out of corners really quickly, but on larger tracks like Daytona, you really need the revs.
I think that the considering how problematic the exhaust port is on a Vincent, it is a good idea to go with torque. If I remember correctly, when Robert did Carleton's head he thought that the D shaped exhaust would be easy and the intake would be trouble. It was just the opposite. He did the intake in a couple of days and it took him a week to do the exhaust port and the D shape went away. I think the concept of the smaller exhaust port was to increase the mean port velocity. Bell says 250 ft/sec and Denish says 280. With a 2" pipe the exhaust loafs around at an astoundingly low velocity, but it seems to work! However, the really fast bikes, like Lindsay Kyle's bike, has a 1-5/8 pipe that is quite short with a megaphone. Ken McIntosh and Lindsay have done a huge amount of development on exhaust and cams.
Finally, it is difficult to make a Vincent rev. Mk2 cams are a 4000 to 6000 cam. There is no reason to go higher, there is nothing there. So, to get back to John, I think the set-up you have will produce a great street bike. It should have lots of power and mountains of torque. I am not sure that I would stray too much from the path.
David