All of our Stage 1, Stage 2, and Stage 3 OEM cylinder heads are now precision ported in-house on our state-of- the-art Fadal 4020 CNC machine in 4-axis!

What does this mean for you? In a nutshell, a new standard of quality and performance! Quite simply, CNC porting allows us to reproduce our best port designs perfectly, over and over, every time.

All CNC ported heads are not created equal! First and foremost, we went to great lengths to ensure our CNC port designs were superb. Using the flow bench, the dyno, and the racetrack, we extensively developed a set of model heads for each application that delivered maximum performance. And then we took it a step further: using the flow bench we identified the best intake and best exhaust port on each pair of model heads and digitized just those ports. The port design data was then mirrored to generate the port design for the opposite head in each case. So in the end, a set of NRHS CNC ported heads actually came out better than the heads they were modeled from!

How much does all this extra effort help? Here's an example. After extensive development, our hand ported XB heads produced an impressive 121 rear wheel horsepower on a 1250cc Buell street bike. This bike was then taken to the Bonneville Salt Flats, and still in street trim, with no additional preparation other than removing the mirrors, it clocked a certified speed in excess of 153 mph. We knew we had a good set of heads for this application. Using the flow bench, we identified the front intake and rear exhaust port as being the best examples of each. We digitized just those ports, mirrored the data for the same ports on the opposite head, and using this profile we CNC ported a set of heads and put them back on the same bike with no other changes. The bike produced an astonishing 124.8 rear wheel horsepower, improving the power over a wide rpm range:

This CNC port profile then became our baseline profile for that application. A similar process was followed for our other CNC port profiles: Twin Cam, Evolution 80", XL Sportster, and Buell Thunderstorm heads. The result is a set of heads that, in each case, outperforms our best hand ported heads, and we can reproduce exact duplicates of these heads over and over. By developing our CNC profiles in this manner, we have achieved a level of performance and quality that is simply not feasible with hand ported heads.

CNC-FLEX - Combining the Advantages of CNC and Hand Porting

We didn't stop there though. While consistency is one of the main strengths of CNC porting, it's also the main weakness, because it doesn't lend itself well to custom configurations. Unless the set of heads being ported is going into the exact same application as the CNC model heads were developed for, the porting will be sub-optimal. This is due largely to the fact that an engine's airflow requirements vary greatly with it's bore, stroke, and rpm, and changing any of these parameters causes a change in port velocity unless you also change the heads to match. Well, port velocity is critical to volumetric efficiency; because cylinder fill goes up as the square of velocity but only linearly with flow, assuming intake close timing that takes advantage of inertial effects to extend the intake cycle. But at the same time, too much velocity creates excessive frictional losses and resultant flow reductions, which ultimately reduces VE . Striking the correct balance is the key, and proper port size depends on several engine parameters as well as the target rpm for maximum cylinder fill (torque peak).

Solving the problem of custom port sizes in a CNC environment took some innovative engineering and resulted in an NRHS exclusive process that we call CNC-FLEX porting.

an example screenshot from CNC-FLEX

CNC-FLEX is an advanced program that mathematically alters key dimensions of the CNC port profile to custom tailor the profile to the target application. The operator simply enters the engine bore & stroke, rpm of the torque peak, cam timing specs, and the valve sizes. CNC-FLEX uses this input in conjunction with the digitized port data to calculate the ideal port size, and then generates the custom porting program which is downloaded to the CNC machine to cut the ports.

In particular, CNC-FLEX optimizes the minimum cross-sectional area found near the short side radius to achieve the desired velocity. Using accepted formulas that relate the input parameters to port velocity, proprietary algorithms adjust this area while maintaining the fundamental port shape as defined by the digitized data. Port shape is every bit as critical as flow and velocity because a good port shape minimizes losses caused by turbulence, keeps fuel in suspension, and efficiently delivers the charge into the cylinder.

The result of all this technology is a combination of the quality and performance offered by CNC porting with the custom capability of hand porting. The best of both worlds!

CNC-FLEX was developed in-house by NRHS's own engineering staff, and therefore will continue to be maintained and improved to reflect new discoveries and advancements in port designs.

An XB head receives the NRHS CNC treatment.

Each port is cut at multiple angles for optimal

matching to the model port size and shape.