Everyone’s heard the saying that cylinder heads make power. While there is a lot of truth to that universal law of engine building, it’s only half the story. Pair a great set of heads up with a mismatched camshaft, and the resulting power curve will reach mediocre heights at best. Take, for instance, GM’s latest crop of LS small-blocks. Their beastly rectangle-port heads move massive volumes of air, but when matched with rinky-dink OE cam profiles, they leave equally massive piles of horsepower on the table.
Consequently, it’s not surprising that a mild aftermarket hydraulic roller cam will typically add an extra 50-75 hp on one of these motors. Furthermore, in the ranks of ultracompetitive drag racing classes, like NHRA and IHRA Pro Stock, he who turns the most rpm often crosses the finish line first. In this arena—rpm, not cfm—is the limiting factor in power production, and efforts to stabilize the valvetrain are ground right into the cam itself. That’s another way of saying that camshaft technology is extremely important, and with Pro Stockers now turning 11,000-plus rpm, that technology has obviously come a long way.
Leading the charge in valvetrain development is COMP Cams, a company that needs no introduction; they have so many wins and championships in the amateur, sportsman, and professional ranks that everyone stopped keeping count. In recent years, the company has spent an obscene amount of R&D and upgrading to the latest and greatest CNC grinding machinery that the industry has to offer. Additionally, these impressive pieces of hardware have been supplemented with state-of-the-art camshaft gauges that can measure a lobe profile to the tiniest fractions of an inch. Combine all that with world-class training and personnel with a streamlined production process, and the result is a staggering rate of progress in a very short period of time. What this means for street cruisers, weekend warriors, and professional racers alike is a balance of power and reliability that the industry has never before witnessed in the past.
To get a better idea of how it all works and how far the industry has come, we had a long conversation with Billy Godbold of COMP Cams. As someone trained as a nuclear physicist, who spends his days pushing the limits of valvetrain development, Godbold is widely regarded as one of the top camshaft designers in the business, and Chevy High Performance was lucky enough to pick his vast knowledge base for your benefit. Here’s what he had to say.
Early Cam Grinders
When I started at COMP Cams over 17 years ago, the aftermarket was using Berco manual cam grinders that were developed in the ’70s. Before the Berco models came about, Norton and Storm-Vulcan both offered manual grinding machines, and some people built homemade grinders. The Berco cam grinders are excellent machines if kept in good repair. The main limitation of these grinders is the quality of the master cam and the care and capability of the craftsman operating the machinery. It was only about 10 years ago when we slowly began making our masters on a Landis 3L machine, but then finish ground camshafts for NASCAR Cup, NHRA Pro Stock, and even CART customers on a manual Berco grinder using the Landis master.
If the limit of a Berco-style manual grinder is the master and machinist, the first limit of a CNC grinder is servo chatter, and the second limit for the aftermarket is cam changeover. The Landis CNC grinders were the first to satisfactorily address chatter back in the ’90s. Their machines are very robust and the servo controls are excellent. We bought two Landis 3L grinders in the late ’90s when an OEM production line closed. These machines were exceptionally good, but our biggest hurdle became changing over from one grind to the next. We also purchased a Toyoda grinder about that same time, but we always had more issues with chatter on the Toyoda grinder; it used very hard CBN grinding wheels compared to the plastic-bonded wheels of our Landis grinders.
All CNC equipment works off error and error corrections. Think of servo chatter as a car’s cruise control, except that it’s more highly refined and accurate to a hundredth of a mile per hour. Imagine you set the cruise at 64 mph and this system taps the brakes just a tad if you hit 64.01, and punches the gas if it sees 63.99. Theoretically, if it reacted fast enough, you could be in for a jerky ride while staying well within even 0.10 mph of your target setting. Servo chatter is exactly the same type of condition. CNC systems use feedback to determine cutting speed. Servo chatter is the condition of the servo overcorrecting on both the high and low side, resulting in an almost faceted surface of the camshaft. The lift profile error is small, but the acceleration error is high. In other words, you are going the right speed, but your neck hurts at the end of the trip.
About 10 years ago, COMP Cams began closely working with Okuma on our grinding needs. Okuma had been trying to introduce their GC34Nh machine in the United States, but needed a partner in developing their machine more for a motorsports and aftermarket focus. Not only was Okuma able to get the servo chatter low enough to allow using the extremely stiff CBN wheels without chatter issues, but they were also able to develop software to take the setup time down from a few hours to about 15-20 minutes. An additional benefit of the Okuma GC34Nh is that these have about half the footprint of the large Landis grinders. It was not long before we had bought a second Okuma grinder, followed by a third and a fourth. This year, we decommissioned our two remaining Landis grinders and have purchased two more Okuma GC34Nh’s for a total of six units.
Most of the aspects of cam design that can be measured well on a $3,000-$6,000 cam checking gauge may be far less important than you might first think. I’m not so sure the engine can tell if there’s a 1/2 degree change in duration or lobe separation from one cam to the next, but other aspects of the cam profile are extraordinarily sensitive to tiny variations in tolerances. These small aspects are probably what kept manual grinding machines so predominant in race camshafts for so many years. It helps to understand that the manual machines tend to try to smooth the master profile slightly just due to the slight compliance of the machine. This created very smooth profiles for use at high engine speeds. On a CNC machine, the profile durations may look near perfect, but the jerkiness of the servos as they respond to error can create an overlapping sawtooth waveform on the acceleration curve. This will excite the valvespring, which isn’t the part you want excited in your engine.
The biggest change at COMP Cams in grinding technology wasn’t the CNC machines that came in the late ’90s, but the first ADCOLE 911 cam gauge that we purchased in the mid ’90s. Management was vehement that we needed to have better measuring equipment before we upgraded our manufacturing equipment. We spent a significant amount on a camshaft gauge, fixtures, and software to bring in the best camshaft measurement system in the world. You cannot imagine how much we learned the first year! Being able to repeatedly measure a cam profile down to the sixth and seventh decimal place, in inches, opened our eyes to a whole new world of possibilities. Actually, we found out that our Berco cam grinders could be far better than we ever imagined if properly operated and maintained, and we learned that changes in the acceleration as small as a few percent could substantially change the dynamics as measured on our Spintron valvetrain dynamics measurement systems.
Small Changes, Big Results
Everything we learned with both our two ADCOLE gauges and three Spintron systems has made its way back into the design and manufacturing side of COMP Cams. Without being able to measure the camshaft profiles and the affect of a profile change on dynamics, I’m certain that our progress would have been drastically stymied. Even in systems that are very stable, we can see changes in duration of 5-10 degrees at 0.050 at the valve throughout the operating rpm due to component deflection. A small change in acceleration or the shape of the acceleration curve can reduce the speed limit of the engine by 200 rpm, and sometimes much more in high-speed applications. While I am not sure even a good Pro Stock engine builder could measure the performance change from even 1 degree of duration, I am 100 percent certain that they could find a way to use an extra 200 rpm if it can be provided without a loss of torque or power at lower rpm.
COMP Cam’s Valvetrain Engineering Group has done an amazing job of streamlining the cam grinding process in the last few years. After a new profile is designed, the information is loaded into our main computer database. From there, COMP’s proprietary software converts the profiles over into a computer code that the Okuma machine can read. Afterward, the cam grinding program can be adapted for any engine family given the desired profile and centerlines. Those part and profile files are then loaded onto our network before getting transferred to the grinding machines by COMP’s expert machinists. It’s important to point out that the same machinists who operated the manual production of our NASCAR cams when they were still being ground on Berco grinders moved across the hallway to our new CNC grinders. As always, the people are far more important than the machinery. Furthermore, the efforts our personnel have made to streamline the process can’t be overemphasized. We have even had guys call about a new cam design and fly down the next day to pick up the cam at one of the local airports. You can now call us on Thursday, build and dyno the engine with a new cam on Friday, and then be on the track Saturday and Sunday.
On a typical run of off-the-shelf camshafts, the variations from cam to cam are extremely small. We allow the duration to move around just over a degree from the original design, but we don’t use any error correction software. The error correction software takes the actual measured specs minus the design profile and then multiplies an error correction coefficient back in. This can get your profile accuracy down into the tenths of a degree of duration, but it can adversely change the acceleration curve. The errors we do measure come mostly from compliance of the camshaft during the grinding process, and this remains extremely consistent from cam to cam. On the manual side, we hold lobe separation within about plus or minus 1/2 degree. On the CNC side, the lobe separation is typically within a few hundredths of a degree from design. Hence, the easiest way to tell if a cam was ground on a CNC or a manual machine is by looking at the ADCOLE report and checking the lobe separation on each cylinder. For instance, if the design calls for 108 degrees and the measured range is from 107.97 to 108.01, then it was ground on a CNC machine. If you measure 107.81 to 108.12 degrees, then it was created by someone doing a very good job on a Berco grinder.
Cam cores come in a variety of materials, and each has its own set of pros and cons during the grinding process. Cast-iron cores are typically used on flat tappet cams and are very easy to grind. SAE 5160 steel is used on roller cams and features a deep heat treat, but it’s easy to burn up if it’s too hard. Similarly, SAE 8620 steel is also used on roller cams, but has a shallow heat treat. It can be prone to burning up as well. Another option is SAE 5150 steel. It works great for street roller cams, but isn’t hard enough to use in some severe-duty race applications. In NHRA Top Fuel, SAE 9310 steel is used for its durability, but its toughness comes at a price. It’s slow to grind except when using CBN grinding wheels. This means that it’s not cost effective for most applications. PM M4 tool steel is another extremely durable material, but it’s almost impossible to grind accurately unless using CBN grinding wheels. As you can see, going to the Okuma grinders with CBN grinding wheels has opened up material options than were not previously available with conventional wheels. The Okuma machines have also reduced or eliminated the biggest issue with materials like 5160 and 8620 steel that are commonly used for roller cams.
Radical cam lobe profiles can really push the limits of cam grinding equipment. Fortunately, our new Okuma machines address several of these issues. For instance, the negative radius of curvature on the cam is supposed to be held at greater than twice the grinding wheel radius. This allows coolant to properly get between the wheel-to-cam interface during grinding. In the aftermarket, that rule is typically stretched a bit, but both burn and push off become much worse as you push the limits. Going to a smaller conventional wheel causes issues with very rapid wheel wear. That’s why a Berco grinder typically utilizes a grinding wheel starting at 18 inches and can get as small as 15 inches, if needed. On the other hand, the Okuma machines have a CBN wheel that starts about 350 mm and has a grinding layer that’s only 3 to 5mm thick. This allows the grinders to start at under 14 inches for more aggressive profiles. Likewise, the wheels stay in a very tight size range for improved accuracy and repeatability. CHP