Reverse Engineering...

[headman]

...
The first dozen head ports I made were programed via RE but the last few have been modeled using a combination of both. CNC porting production based heads with cast finished port sizes on thin wall castings pose issues with core shift and I find that RE works better in those applications.

Richard

Thank you for bringing that aspect to the table.
From experience "remachining" parts, I knew that seldom is anything ever exactly where it should be.

[SchmidtMotorWorks]

I find that RE works better in those applications. Too often the ports have untouched areas along different sides.

Hmmm, I don't understand why, is it that the castings vary? Usually all the ports on one side of the head are on one core so I would think in most cases it is just a matter of centering up on the ports.

Anyhow, I don't understand how RE plays in to that issue either positive or negative, it seems to be a matter of the design and the positioning. What am I missing?

[richard@wcch]

I've seen castings shift over .060" from one core to the next. The same casting numbers of the same type of heads. Core shift drifts directions in 3D space. I use RE to help me make the port cross sections stay as small as possible yet still allow me to clean the port surfaces. Otherwise entire port sections aren't touched by the tool. Increasing the port cross sections to cleanup all surfaces would result in a very large finished port or combustion chamber and this is a detriment to airflow or compression.

Richard

[Ron E]

Not sure what's "shifting", but .060" wall thickness differences from one to the other end of a head not a shocking thing to find.