The Art of Airflow

Engine porting has been around for as long as there has been electricity to power high speed grinders, but there are many options a racer or street buff can choose from when looking to improve the flow rate of a given part. When talking about airflow, two of the most popular components to port or improve are the intake manifold and the cylinder heads. Most cylinder heads today are made from aluminum and perform very well in their stock form; however, when ported and polished, these components can be improved dramatically and gobs of extra power can usually be expected.

Cylinder heads and intake manifolds today are shaped very differently than in years past and most port configurations have shapes that are hard to reach with a conventional grinding bit. The old "tried and true" way of porting consisted of grinding a given amount of material away from the port of the head or intake until a desired shape is met. From there you can determine if the component is better or worse by track-testing the car or flowing the part on a flow bench.

The problem with hand porting is that no matter how experienced the porter, it's very difficult to make all eight intake and eight exhaust ports exactly the same. Some ports might be shaped differently due to the location of the intake manifold runners and some ports might vary due to the inconsistency of the porter. But make no mistake about it, hand porting does work and, if done with the proper care and knowledge, can be one of the most effective ways of improving the horsepower of a given engine.

The wonderful world of computers soon brought us CNC machines. A CNC machine is a device that sort of looks like a drill press but uses a grinding bit instead of a conventional drill bit. A cylinder head is then bolted onto the table of the device and, with the custom programming of the computer running the grinder, it can port an entire head all by itself. A computer design will move the grinding bit upwards, downwards, side to side and even in custom angles to perform the job.

CNC machines have brought the porting game to futuristic levels of achievement and nothing can match the quality and consistency of such a device. Picture being able to design and test a given port design on a computer before testing it out on an expensive racing head. Not only that but a CNC machine can modify a port (on an intake or head) with frightening accuracy. But, just like with hand-porting, there are disadvantages to such a luxury. Even though CNC porting is unmatched by today's technology it comes with a pretty hefty price tag. These machines are extremely expensive to purchase and the end result is that you, the racer, will wind up paying a pretty big sum of money to have your heads done. There are companies that offer CNC-machined heads already finished but it is still an expensive procedure. With that we turn our attention to yet a different process of head/intake porting, which is known as the Extrude Hone process.

Putty For Everybody!
Extrude Hone is a company based out of Irwin, Penn., and they take a totally different approach to making heads and intakes better. They use special machines to pump abrasive (media) through the ports to make them bigger and better flowing. "In its most basic terms, the Extrude Hone process can be thought of as a grinding stone that has come alive," explained Rick Miller, the automotive project manager at Extrude Hone. "The media used in the abrasive flow process acts as a self-forming file that will conform to the exact shape of the surface or passage that is to be processed.

Polishing, deburring and edge radiusing are accomplished anywhere the media can be forced to flow. The end result is a surface finish quality (the port) that cannot be matched using traditional porting methods. Inaccessible areas that were previously impossible to reach are typical applications for the Extrude Hone process. Materials from soft aluminum to tough nickel alloys, ceramics and carbides can be successfully machined using our unique process."

In simple terms, the Extrude Hone process basically pumps a harsh and abrasive media compound through the port of a head or intake and the sand-like media smoothes out the port to make it better. The end result is a smoother, better flowing and cleaner finish. When discussing the advantages of the Extrude Hone process two things come to mind. For starters, the process is not expensive and ports that grinding materials can't reach are no problem for the pressurized media. The stuff can go anywhere air can go. There are no limits to its capabilities and that is why the process works so well.

Another advantage is that certain intake manifolds need to be cut in half due to their awkward shape and size in order for the porter to be able to access the inside of the unit. If the intake is not cut in half portions of it will not be able to be reached by a conventional porting tool. This is no match for the Extrude Hone process as the media can be pressed into virtually any shape. This also saves the intake owner the hassle of having to weld the intake back together after the porting job has been completed.

"The central element of the Extrude Hone process is the media, a polymer carrier mixed with abrasives. The viscosity of the carrier and the abrasive grain size, type and concentration can be varied to achieve specific finishing results," stated Miller. "When forced into a restrictive passage, the viscosity of the media temporarily rises, holding the abrasive particles rigidly in place. The media abrades the passage through which it flows only when in this restricted state. The viscosity returns to normal when the thickened portion of media exits the restrictive passage, producing no abrasion on areas such as threads or seal surfaces.

The tooling to perform such a job is equally impressive and very important towards the accuracy of the job. "The tooling holds the work piece in position and directs the flow of the media to the required areas," said Miller. "Many applications require only simple tooling: dies typically need no special tooling; the die passage itself provides the restriction for the flow path. For external edges or surfaces, tooling is used to restrict the flow between the outside of the part and the inside of the fixture. The tooling may also serve to restrict flow through areas that are to remain unaffected.

The Extrude Hone process is operated by a machine that is available in a variety of sizes and configurations. "The typical machine contains two vertically opposed media cylinders which hydraulically close to hold a part or fixture between them," explained Miller. "By extruding the abrasive media from one cylinder to the other, a honing action is produced wherever the media enters and passes through a restrictive passage."

We currently have two separate components that we were hoping to improve on. The first is a set of Cobra cylinder heads that will be going on a 10-second blown street car in the near future and the second is a Bullitt intake that we plan to plop to our latest supercharged 2-valve project, the Ice Box. The car recently ran a 12.65 at 111 mph with the stock intake in place (on Nitto 555 street radials), but we feel that the improved Bullitt design should lower that figure significantly.

We wanted to have both of the components professionally ported prior to the installation and felt that the Extrude Hone process was our best bet. We had Rick Miller perform his magic with the media solution and before long we were rewarded with an extra 20 percent of airflow from our Cobra heads. The heads flowed a fair amount of air in stock trim but increased dramatically with the Extrude Hone process.

As far as the intake manifold went we had a small problem adapting it to the Extrude Hone SuperFlow flow bench but Rick was able to calculate some percentage figures and the gains that we were rewarded with were 10 percent better than stock. Not bad for a simple media process and our Vortech-blown '01 GT should really respond to the bigger and smoother Bullitt intake.

The Extrude Hone process has taken cylinder head and intake manifold porting to new and exciting levels and is even very affordable to do. What's even better is that a head or intake that has already been hand ported can still benefit from the Extrude Hone process. So next time you look inside your wacky and contorted intake manifold and wonder how in the world you can improve the flow rate of it, think Extrude Hone. It's the best choice you have.