Unlike Jay's experience, I have cartridge rolled several CNC heads for folks over the years and the flow remained almost exactly the same--less than 3 cfm difference, which can be attributed to exact placement on the flow bench fixture. I have bought CNC heads for myself on occasion when I needed a pair for an engine build, and I didn't have time to port them myself. I decided to do a quick cartridge roll to increase the flow like everyone says, and I wasted several hours when it was all said and done. I don't think it hurts anything, and if anything it actually is beneficial. I frequently get requests from a couple of shops in town to flow a CNC'd head for one of their customers, and give them an actual flow sheet on that head. It gives me a chance to see all kinds of heads from Pro Stock to heads like the ones I flowed last week that were DEAD. I have flowed the new Motorsports D-3 CNC'd heads that went 410 cfm on the intake with a 2.135" valve, and those ports still had cnc marks in places where the original shop did not think it necessary to completely blend the ports smooth. If you buy a set of CNC'd heads, run them with confidence after you thoroughly clean any loose chips from around guides, or valve stems. Some shops run their CNC program without the guides installed, and then install the guides afterwards and do the valve job. Those usually are clean enough to run as is. Joe-JDC
