The angle on the valve and seat on the 928 is 45 degrees. I have been reading a bit on performance and longevity issues and there are some recommending a 46 degree angle on the valve seat and a 45 degree angle on the valve. This is supposed to reduce the surface area and reduce heat on the valve. I could see this on intake valves as they do not get as hot, but I would think one would need more surface contact on exhaust valves to cool them.

Any input on this? Unless there was a good case to be made I am not sure I am up to trying this on a 928, but I am wondering if anyone has considered it.

 

Rule of thumb has always been 1 or 2 degrees different on any valve for better sealing.

 

I see nothing in the manual - both the valves and valve seats are at 45 degrees. I am more curious if anyone has tried changing the angle on the 928.

Another issue is lapping. When I talked to the people who sell cutters they did not advise lapping. I am curious if lapping is no longer considered valuable.