Originally Posted by ssmonty
The ridges around the valve seat inserts were not swirl devices. Some chambers on the head had them and some didn't. It was left from the machine operation at the factory to install the seats. I believe a machine operation be it by CNC, or manual mill, or something else was used to cut the bore to the same depth for each chamber relative to the table height of the machine. However each chambers casting depth wasn't consistant thus the ridge on some chambers and not on others.
If your refering to a vane downstream of the valve guide, there wasn't one on these heads. I did reduce the diameter of the guide bosses to reduce air flow restriction although it won't make that much of a difference, similar to the reduced valve stem diameter of the Manley "Pro Flow" valves I installed. I figure every little bit helps as far as beating the next guy.
If your refering to a swirl vane in the chamber such as a raised boss around the spark plug location, there wasn't one in my heads.
As far as a "Rule of thumb for aftermarket heads is only port them if you have too by class" thats the first time I've heard of that. I have heard of no porting allowed in certain classes. As far as I'm concerned I had the spare time and the will to try to make them better than stock before I installed them on an engine vrs removing them to do the same later.
To each his own,
Some types of racing require stock or limited port volume. In that case specail concerns need to be address as everyone else has done the same. For racing go for broke.
Lip around seat from steal to alum needs to be cleaned up but can have little effect if seats were installed correctly.
Yes they cnc the heads but do not cnc port the heads its just part of the manufactuing process. Cnc porting cost extra.
The reason not to port aftermarket heads is they do produce the numbers unmolisted. If you have an issue with the head you cant send it back if its cut. Also if you need more flow just buy a head that is desgined to flow more. Get 210cc heads or 234cc heads. Dont buy the smallest port head and try to make it bigger its not that simple. Cutting the heads will most likely end with less flow. Many engine builders are looking to add metal to the heads. Just removing metal wil not increase flow. Also on stock heads there are many reasons to remove a little metal to clean them up. Casting marks and bumps that can be removed to make more power. On after market heads they cast them with good ports so its not likey there is any power to be had with easy port work. If so they would do ot before they ship it out.
Swirl devices are on the port roof and split by the guides. Depending on which way the air swirls around the valve. Ypu have both side cut the same and it does not flow that way it flows around the valve.