Mongler, thank you for your recommendation.
That porting youtube is not what I would want to follow, but as the producer of the video says, there are differing opinions. The point with port wall finishing and most specifically, extrude hone finishing, it CAN cut in places that make the flow improved, and most definitely can cut and polish in places otherwise unreachable. But a mirror finish is NOT the right finish.
I made a post called 'Porting Porn', about 2 1/2 years ago, that was really given some sarcastic treatment by several self-proclaimed porting experts, and a member or two with an axe to grind... I was willing to show some of the angling and shape of the port. The reason for shiny; the proper finish in a video or picture would look flat and shapeless without the glint of a shined up port. The reflection displayed the shape. I might note, the self-proclaimed porting geniuses will take shots at me, but not give any pictures for their own designs. Instead, one in particular hijacked my post to advertise themselves.
The single most important bit of information about surface finish was given to me by a recently passed porting genius, Wade Newman, who worked for Dart for decades. I call him 'genius', as he performed the porting work on 4 different engines that set records in their respective classes. THAT is a man you can trust about porting. When I asked him most directly about porting finish and ceramic or other heat shielding coatings, his answer surprised me. "Whatever finish you use, the heat shielding company will change the surface. But it really doesn't matter. The more important issue with heat shielding is to carry the heat out of the head, where is does more good than any loss in port finish by spinning the turbo."
He also informed me of the method and reasoning behind what some call 'port match', which should really be called a 'reversion stop'. As one of the porters illustrated, under certain flow rates, a drop of water will be sucked up into the port, even though the flow is going out, which is the exact description of 'reversion', in a cylinder head. There is a simple trick to compensate for that. We use it. Thank you, Mr Newman.
We know other porting masters, and I do not claim that myself, as I am always learning, but when porting, and considering flow, it's a bit of a stretch to think maximum flow is the ONLY thing...it's not...unless your only interest is to run the engine for maximum performance all the time and therefore air speed... drag racing for example.
So also, that applies to valve seat preparation, as the engine under normal loading could never take advantage of a 7-angle seat cut. Even then, I really doubt there is much of any advantage. We regularly use a 3-angle cut. Even increasing valve dimension is a bit dubious under all but the highest performance situation. There is an issue of shielding on the intake we think does not help.
To get to the precision, matching port to port is something people claim you can't do, cutting by hand, and I disagree, within limits. We have used our Bridgeport to match depth of cut and radius, which helps a lot. Working within the exhaust and intake gaskets, you can get a better match for volume cylinder-to-cylinder.
If we ever get by encoder issues, maybe I can do some digitized porting. That would help more than anything, as the port size matching is a function of the machine.
