Most engine builders are in agreement that one of the most efficient ways to improve the airflow volume and reduce turbulence through your engine is to optimize the shape of the intake and exhaust ports of your cylinder head through machining. In the early days of the horsepower wars, port shaping was done entirely by the steady hand of a machinist, and while this was the best method available at the time, it left a lot on the table in terms of accuracy and consistency — and ultimately horsepower.

In the decades since strictly hand porting performance cylinder heads was the norm, the world has experienced several technological booms that have brought welcome change to both manufacturing equipment and computer technology. Which eventually led to the two industries merging to create Computer Numerical Controlled (CNC) machinery.

To learn a little more about hand porting’s relevance in today’s world and the advantages of modern CNC porting practices — in comparison to the approach of our racing ancestors — we sat down with cylinder head gurus Jonathan Waitt and Shawn Hooper, CNC Instructor and Cylinder Head Instructor, respectively, for the School of Automotive Machinists and Technology (SAM Tech), and Tim Torrecarion, Director of Marketing for Air Flow Research (AFR).

A machinist for Air Flow Research operating a Haas CNC machine.

Modern CNC Porting And Valve Seat/Guide Advantages

With the advent of CNC machinery, high performance cylinder heads are being flow optimized in a fraction of the time it took by hand and with far superior accuracy and consistency from port to port or seat to seat.

CNC porting a head takes a job that may have taken weeks to do by hand in some cases, and turns it into just a few hours.                     -Shawn Hooper, SAM Tech

“A CNC machine will happily repeat the exact shape of the port and combustion chamber over and over again with far greater accuracy. This does away with potential inconsistencies that could arise from manually porting a cylinder head,” explains Jonathan Waitt, SAM Tech’s CNC Instructor. “You also significantly reduce the amount of time that it will take to have a finished set of cylinder heads. A set of heads can be done in few hours on a CNC machine, while a thorough manual porting job could take at least several days.”

“The biggest advantage that CNC porting provides to a manufacturer, like AFR, is repeatability and consistency from one port to the next. The second advantage would be the reduced time and long-term cost,” says Tim Torrecarion of AFR. “As a cylinder head manufacturer — by eliminating the need to shape each port by hand, CNC machines have allowed us to vastly increase our unit [head] production numbers each day. In addition, we also have the ability to keep the machines running 24 hours a day, 7 days a week, and 365 days a year if need be.”

A small portion of Air Flow Research’s machine shop in Valencia, California.

“CNC porting a head takes a job that may have taken weeks to do by hand in some cases, and turns it into just a few hours. Another huge advantage is it will also remove any flaws that the casting may have — like core shift — making it much easier to verify that every port is exactly the same,” states Shawn Hooper, Cylinder Head Instructor for SAM Tech. “One thing many people overlook is the fact that just because it is cut on a CNC machine doesn’t make it perfect, many times there are advantages to coming in and hand finishing the port. If you don’t design a good port to start with, you will not get a good port after it is cut on a CNC mill.

Dexterity Still Matters!

A SAM Tech student porting a cylinder head by hand. [Photo courtesy of Stephen Kim]

“Many times, those CNC milled heads actually started out as a hand ported job that was then digitally scanned and turned into a digital CNC program,” states Torrecarion.

“There is software available to machinists that can dictate Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) data for cylinder heads, but the hardware and software is typically too cost prohibitive for your average shop to be able to purchase,” says Waitt. “You would most likely find it in use only at the big OE manufacturers and top-tier engine builders, while the majority of the aftermarket racing industry still uses a flow bench and a highly skilled manual cylinder head porter.”

“The cylinder heads being designed by hand simply rely on a grinder, years of acquired skill, and a flow bench,” states Hooper. “For CNC heads, once we have decided on a port design that we want to use, which can require many programs for one head, depending on the application. We will then digitize that port and use a program like Mastercam to take that data and write the tool paths.”

Port (left) and combustion chamber modeling (right), using computer aided machining design (CAMD) software. [Photos courtesy of Stephen Kim]

“I honestly don’t think hand porting will ever be entirely phased out, unless the cost of the technology and equipment is significantly reduced to the point where your average enthusiast can afford to produce their own CNC parts at home,” says Torrecarion. “And for the smaller businesses and manufacturers in our industry, the upfront investment required to purchase the CFD software needed to digitally design and test ports is just not realistic for them. And that’s prior to even creating the CNC program for the machine!”

Every Manufacturer’s Approach Is Slightly Different

“The main goal for us at Air Flow Research is to make sure that the engine combination our customer is building will meet all of their expectations — whether that build is a street cruiser, a nitrous fed drag car, or a boosted road racer,” explains Torrecarion. “When we’re approached to design a cylinder head, we will first ask a number of questions such as; engine displacement, the intended purpose of the build, the weight of the car, camshaft specifications, and desired RPM range for example.”

“Once the best cylinder head design for that application has been chosen, our team will get to work machining the head on an array of Mazak, Mori-Seiki and Haas CNC equipment, where each work station has a check list of items they are required to complete to ensure our quality control standards are met before any heads make it out the door,” concludes Torrecarion.

“For SAM Tech’s cylinder head program, [like AFR] we first start by figuring out what the head is going to be used for — application, engine size, RPM range, and even class rules if necessary. Then we always begin working on the guide and seat work first,” states Hooper. “The whole port revolves around what size, depth, and angles you use for the valve job, so this must be set before any other work can be done. Then we will set up a gasket match, taking into consideration variables like what valvetrain you will use, what intake type will be used, and if it must retain a stock port location.”

“As for the visualization, a port mold is a simple way to get a good measurement from the port. We also can slice the port after it has been digitized to make sure our dimensions are correct,” says Hooper.” As far as CFD goes, we will use this software when we come up with a design in SolidWorks for things like intakes and runners. It’s important to remember that these are still just tools, and the software that is available to the majority of the public is far less capable than what is used by many of the OE automotive manufacturers.”

“Over in SAM Tech’s CNC program, once the cylinder head passes the head porter’s criteria it is then turned over to our CNC department. Once there, we scan the cylinder head and make a digital copy of one intake port, one exhaust port and a single combustion chamber using a FaroArm inspection and analysis machine and Verisurf 3D modeling software,” says Waitt. “The FaroArm is a portable Coordinate Measurement Machine (CMM) that records the shape of the ports and chamber.”

SAM Tech uses a FaroArm coordinate measurement machine (CMM) to digitally record the shape of the port and combustion chamber to be visualized using 3D modeling software. [Photos courtesy of Stephen Kim]

“After we collect all of the digitized information for the head using the FaroArm, we can then use Computer Aided Design (CAD) software to create 3D models of the ports and chamber,” continues Waitt. “Using the Mastercam Computer Aided Machining Design (CAMD) software we are able to dictate how exactly the head will be cut in the CNC machine, and once the orientation is set we apply tool paths to cut the ports and chamber. With the tool paths done, our team will then run a simulation of the machining process to verify that everything is cutting correctly. Once verified we can transfer the program from Mastercam to the desired CNC machine, and we are finally able to start porting cylinder heads!”

The Takeaway

Large manufacturers like Air Flow Research are able to eat the initial six-figure (or higher) investment for the latest CNC machinery and the associated software. For a manufacturer, the machinery will pay for itself in the long run by greatly increasing daily production numbers, improving quality control, and reducing the labor hours required for each job.

But, as long as the up-front cost for CNC machinery and its software stays outside of the financial reach of your average performance shop or even enthusiast, there will always be a need for highly skilled machinists who take pride in porting cylinder heads by hand and relying on a flow bench.