I've read bits and pieces of info here and there stating that this is something that the "high end" guys do to squeeze out the last few ounces of airflow that couldn't be gotten by the CNC due to the limitations of the cutting bits to produce the smoothest desirable surface finish in a port. On the average, how much airflow could one realistically expect to gain by doing this?

Lingenfelter offers this option and I've always been curious how beneficial it is. I'm equally curious about how much could be gained out of a set of Ai 200cc heads. (290cfm@.600 out of a 202-203cc port possible?)

How much of a restriction are all those tiny little ripples?

 

IMO, it would only be something a hard core racer would do and be done by someone who was very experienced.

 

Nothing in taking out the tool path if it's done well. In stuff that you see on mass produced CNC tooling where the different tool paths come together and don't quite meet up, then there is a need for it.

The only limitation sometimes is how tight of ball end mill you can cut with and sometimes that can't cut the shapes that are needed so hand finishing is done there.

Very good CNC race heads will have some work done to the short side radius anyways and blending the valve job in.

Bret

 

Thanks for the reply Bret. In reference to your comment about the short side radius being addressed, I did a little more digging, and it seems that this is a detail that splits the difference between 3-axis and 5-axis CNC's. Apparently, a 3-axis just can't "reach" that area of the port very well.

Even if there isn't a whole lot to be gained in performance over 5-axis porting, the hand finished one sure is alot prettier to look at:

 

I did that on mine. Didn't change the shape on anything, just blended the machining and casting areas a little since they were like 70% CNC to begin with. So I mainly knocked off burrs and casting flash and polished my exhaust ports some.