Manifold Port Match - Details...
To ensure the best possible port match, the head, intake manifold, and plenum should all be bolted together, and ported as one. In addition, they should all incorporate some sort of doweled alignment, to make certain they are in fact consistently aligned, EVERY time they are bolted together.
Once the parts have been "doweled" and bolted together, their relative positions, will ALWAYS be the same, and the port match can then be successfully performed. Without this, the shuffling will cause miss-alignment.
The "doweled" assembled intake, (manifold, plenum, head), are all bolted, together, and their positions scribed onto each other. From there, the ports are designed, re-scribed, and opened up with the proper porting tool(s). Whenever possible, the actual "porting" is done while everything is bolted together, making all the openings align perfectly. An "edge break" is made to the delivery port, while a "de-bur" is made to the receiving port.
The individual components are once more dis-assembled, lapped flat (by hand), prior to cleaning, then are thoroughly cleaned, again, to remove chips, machinist ink, and cutting oil.
95% of ALL the porting shops will do what they call a "GASKET MATCH/PORT MATCH". In most cases, this is a big mistake. Some import auto makers (particularly Nissan), went through the trouble to make the receiving manifold port slightly larger, often with a nice .020" flared taper, anticipating some port mismatching. Further more, the gasket is 2 millimeters larger than the port. Even if someone performed an accurate gasket match on all 16 holes, the loss of port velocity created by the larger cross-sectional area would negatively effect the flow by slowing down then re-accelerating the intake "pulse". This results in more than simply loss of flow, it can and will damage your "pulses" even more than most simple miss-matched ports. The intake and exhaust tract both "pulse" their flow, and "irregular" beats within this "pulse", rob power, cause flat spots, and can induce turbo lag.
Consider also, the alignment of heat spacers used in the intake system, most of which require work, as to "not negatively impact" intake flow due to poor quality. The heat spacers from "A Large Unnamed Supplier" are status quo of their poor efforts to meet acceptable quality standards. A few years ago, they flew me out to their business, to help them correct their renowned quality "issues", however, their offer did not reflect a real seriousness to do so, and they seemed to be content to serve the masses, who don't seem to know the difference in quality, or are content to accept "China" quality, with "Taiwan" prices.
We strive for "Perfection Per Application" and every job begins and ends clean, as if every part, was the ONLY part we were working on.