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Ben,
Most people reading this may think I am saying not to port your own heads because I want the business. Not so. I have more head porting orders than I can keep up with and could very nicely limit my head porting to doing heads for the engines we are putting together. And I definitely want to eliminate the business of fixing heads that others have screwed up. Usually takes me more time to "fix" one of these than to do a head from scratch. Right now about 30% of the heads I am working on are in this category, and I keep swearing I will not do another. Then someone sends me a head to test that they ported, or had ported by someone locally. I test it, find problems, and they plead with me to fix it.
So basic advice is: If you do not have a flow bench and access to a dyno to check your results, don't port the head. Also do not take it to anyone to have ported who cannot show you the flow improvements on a flow bench and dyno results of other B18/B20 heads he has ported.
The key problem with giving simple advice is that its not a simple matter.
There are actually 8 different ports in one of these heads - lefts, rights, insides, outsides. Further, each head is cast a little differently due to core shifts in the casting and the fact that a head actually consists of two sections that are not always joined the same. Due to the casting shifts the machining at the valve and intake manifold face are not in the same relation to the port on each head. You don't see this until you have about a half dozen heads sitting in front of you and examine them carefully. So, in essence, a lot of what has to be done is correcting casting differences to try and bring that port up to an optimum standard. The above is a long way of explaining that you can't do the same thing on each port. Work that will improve one, will hurt another.
Any changes that you make have to work together. Improving one area of a port without making an equal change in another can cause the flow to become turbulent, separate from the port walls, with the result that the flow is reduced. This often happens with doing anything to the intake, including smoothing out the flashing. One reason that you need a flow bench to check your work.
For a street engine, don't bother trying to match the port to the intake/exhaust gasket. Its a waste of time and will only hurt things. Just be sure that the exhaust is smaller than the manifold its flowing into and that the intake port is larger than the manifold that is flowing into it.
Can't really tell much from the photo. But the real problem is that the valve seat has not been done. The area from the seat to the area of the port below it, the bowl, is critical. So without a seat its hard to comment.
Quick advice on the exhaust is to do a three angle valve seat (30,45,60) and blend it into an area just below the seat that is approx. 1.150" in diameter. For best flow the actual 45 deg. seat should be approx. .050" wide. Back cut the valve at a 30 deg. angle. Do not spend time rounding off the inside radius as it is easy to hurt the flow by doing this. Do this work at the same time as hardened seats are being installed.
Quick advice on the intake is to leave it alone. Use an injected head, as they flow 10 - 15% better than the carbed heads, depending on the exact casting.
And use one that does not have large core shifts to begin with.
John
V-performance.com
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