My cylinder heads are in getting polished and rebuilt. SHould I pay the extra $50 to match the cylinder exhaust ports with the headers? Is it worth it? Thanks
Why would you match the heads to the headers? Most header flanges are so roughly done your ports will look like crap. I would have them match the ports to an exhaust gasket that closely matches your header flange, then match the header flange to the gasket while cleaning up all the boogers.
Matching ports is most often done using the gaskets as the template. I would assume that the headers are matched to the gaskets or that the flange is already slightly larger (which doesn't hurt anything). The important thing is that you don't want any part of the flange or gaske in the way of the flow from the head.
paul is right, you don't want the gasket or flange restricting the flow of the gases. But 99% of the time, the header, gasket, and flange are larger than the port (especially true on stock heads)...meaning that you can't open up the port in the head enough without running into water jackets. In that case, it's best left alone. A header/flange that is larger than the port can help a little anyway
Mavman, You can open the ports (on a 289, 302& 351) to the size of the gasket opening without hitting water. You can then blend back into the port 3/4" to make the flow smooth. I have two of the heads that I have done waiting to go on a 351W. The header port is usually larger than a standard exhaust gasket but you can always relieve the outer edges if it is too close for comfort.
Be sure that the exhaust port is still a bit smaller than the header opening. Roughly 1/8" should be fine. This will enable the cylinder head face to act as a reversion dam.
