Rpm 340 Cyl heads on a 318 !

I’ve seen that number (.060) for valve shrouding before. I haven’t been there myself. Just witnessed work being done. (For those who don’t know...) While making the clearance effort, the work done wasn’t a simple clearance cut but a reshaping of the cylinder heads chamber around the valve that has metal too close to the valve. It is a simple thing to do. The main two focus points are;

1: Removing material from the chamber around the parts closest to the valve to allow the air and fuel to get passed the valve with a path that will not allow the air and fuel to crash into the cylinder head.

2: When the material is removed, create a smooth pathway. Do not leave a wall anywhere. Reshape it smooth. It doesn’t have to be polished. Just lay it down. Remove only as much material as needed. There is no need to get wild or creative. The reason being is that once that valve opens up passed the angles of the valve job it is given, it no longer becomes a concern since all the air flow there on is no longer inhibited or facing any obstruction. The rest of the heads flow while the valve is being lifted passed that point of the valve job and the now missing obstruction of the wall in front of the valve that is now gone is the work of the bowl and ports.

The work I seen done was with a tiny flap wheel. IDK what cfm gain there is but the real gain is the quality of the air and fuel entering the chamber. If you could put a number on the cfm gain, lets just say is 8 cfm, your not going to see a rise in power directly related to the increased flow number but more since the (again!) QUALITY of the air and fuel mix is much better.

If anybody is faced with this, I’d recommend you give it a try. It’s of hard to do and I can be done in a short time.