[NickD]

Has anyone ever heard of back cutting valves? From what I have been reading it's a process where you sort of "polish" the backs of the valves where the valve seat is to increase air flow over the valves. Is this something done strictly for racing engines?

 

[CWA-94GS]

I have seen where they apply abrasive paste to the valve, push it into the valve seat and then turn it a bunch of times. This insures a good valve fit into the seat so it will seal properly when closed. The smooth surface would be good for airflow but I think the sealing part is most important if the valve is not airtight when closed you will lose compression. I think is called valve lapping