CNC Porting frequently asked questions…
How is CNC porting different than the traditional means of porting?
CNC porting is very precise because it is computer conrtolled. We can calculate the required cross sectional area and machine the port to that dimension every time (within less than .001”). We can also maintain consistent size throughout the port. Therefore, each port in the head will be identical and every ported head will be the same. This is a huge contrast to porting each head using grinding and sanding tools by hand.
Is there a noticeable difference for the average street rider/racer?
In the past, the average street port was just a basic clean up (less time, lower cost). The pro style port job was very time consuming (sometimes as long as 3-4 days) and much more expensive, while still having the inconsistencies of handwork. The CNC machine does not care if it is cutting .001” or .100”. Consequently, the street rider/racer can get a precision pro style port job in much less time, and priced somewhere between the cost of a hand pro port and a hand street port.
What are the benefits and disadvantages of CNC porting over turbo charging or nitrous?
CNC porting benefits normally aspirated or forced induction/nitrous engines. There are some classes or forms of racing, which do not allow turbos or nitrous, making porting a necessity for finding extra power.
How long will it take to port a cylinder head with a CNC?
The average inline four cylinder head takes between five and seven hours to CNC port. We put considerable time and effort into getting the program complete for each type of new head we choose to CNC port. While net flow was what head design was based on for many years and it still has some importance, there are many other important factors we now know we must take into consideration. We must first calculate the cylinder head requirements (power output, RPM range, bore, stroke, etc.) to get the desired cross-sectional area and flow in the port. We use previous experience and engine-modeling software to calculate required flow/air speed in the port. We then fixture the cylinder head in our five-axis machine to get all critical locations (intake spigot, exhaust spigot, valve seat, valve guide, etc.). We then hand port the prototype port & flow test until we reach the goals we have previously calculated. The early-on CNC technology stopped there. Many shops still hand port the head and input that information into their CNC, copying the hand port. We go many steps further in the process. After the prototype is finished, we then digitize the actual port surface. After we have an accurate port model, we can make measurements of the actual cross-sectional areas throughout the port (every .050”). At that point, we can make adjustments in our CAD drawing to specific areas of the port to maintain consistency and match minimum cross-sectional area goals. Once we are happy with the final port size and shape, we align the model with previously measured spigot and seat locations. We then create the program to duplicate the final ports in the head. We amortize the cost of the above time/labor over the estimated number of heads we think we may port in the next couple of years to determine the porting price.