FAQs With the Top Minds in Valvetrain Development

Words: Cam Benty

Valvetrain prep, on the surface, would appear to be a fairly straightforward topic. You pick the right parts as described by the guy on the tech line, check the specs on the parts when they arrive, degree the camshaft, and away you go. But, the reality of picking parts and setting them up correctly to get the best performance and durability is not always as easy as it may seem.

Valvetrain

We sat down with two of the top valvetrain engineers in the business, Billy Godbold from COMP Cams and Jerry Clay from Crane Cams, and asked some questions commonly misunderstood by engine builders and enthusiasts. Most interesting to us as we assembled this story was we found the “easy” questions were not so easy and packed to the valve covers with surprisingly new information. Read through the following, and we bet you’ll learn something along the way. We certainly did.

How do I set hydraulic pre-load?

Godbold: The best method is to have a dial indicator on the back of the rocker above the pushrod as you tighten down a non-adjustable rocker or set the preload on a stud mounted rocker. In this way, you can determine the real preload amount without having to think about turns per inch or how much the ratio changes the pushrod movement when you turn a bolt in the trunnion.

For the record, a quarter turn is about 0.010 to 0.013 inch, and a half turn is about 0.020 to 0.025 inch of trunnion movement, but the pushrod preload would be about 50 percent more at that end, due to the fixed valve tip position and rocker ratio. I like about 0.020 inch preload in most applications, but you can measure it much more closely with the dial indicator.

However, counting the turns from the point where the pushrod begins to load to the lifter piston bottoms out is also very good.  Using this technique, you know the total adjustment range and can choose between the standard performance light setting (1/4 turn down), the typical OEM setting of mid-travel, or go to a longer pushrod and run it close to the bottom to minimize oil volume (and, thereby, oil bubbles) by setting the preload three-quarters of the way to the bottom.

Camshaft Degree

As you might have guessed, degreeing the camshaft is critical to achieving peak engine power and torque. But if you use lobe centerline when determining camshaft position, you could be doing it wrong!

What is the most common mistake you find with engine builders these days?

Clay: The challenge of getting the camshaft degreed properly is well documented, and the downside of not setting up the camshaft correctly should be motivation enough to spend the time required to get it right. But complicating the camshaft degreeing process these days is understanding that camshaft lobes are not symmetric. Translation: The opening and closing ramps are not the same. As such, determining the centerline of the lobe is far more difficult. If you are degreeing your camshaft by noting the centerline of the camshaft, you could be a half to a full degree off. For that reason, you should always degree your camshaft at 0.050-inch lift. All camshafts come with this spec, so there is no reason to ever use centerline measurements again.

Full-travel or short-travel lifters — how do I know what is best for me?

Godbold: Assuming you read the preload description in the first question above, you will note there are good reasons to choose light, mid, or deep preload settings. Knowing there are benefits to being 0.025 inch from the top, in the middle, or 0.025 inch from the bottom, you can quickly deduce why a short-travel lifter can put you in all of those positions at the same time. The negative is you either are required to run a very specific pushrod length or an adjustable rocker system.

Short-travel lifters will always outperform the full-travel lifters, but in many applications, the slight improvement in performance may not outweigh the time and cost to get the preload so close.  On the full-travel lifters, you have over 0.100-inch range of preloads, and anything from 0.020 to 0.080 inch preload will perform more than adequately for most applications.

When building an engine, what are the critical dynamics to consider when selecting valvetrain components?

Godbold: Component mass, stiffness, and natural frequency are the three main focus elements in valvetrain component design. While looking at these parameters at the component level, we must also consider how the entire System Effective Mass and System Stiffness will respond to changes at the component level. Also, the driving frequencies (from the cam profile) need to be considered.  Going to a very good, but heavy rocker on a light system can be a bad choice, even with an excellent component. Looking at the systems approach is paramount for good dynamics.

How does compression ratio affect camshaft selection?

Clay: The key factor to consider here is cylinder pressure. If you have a lower compression motor, say 9.5:1, and you use a camshaft that is fairly large (increased overlap between lobes, which allows both the intake and exhaust valves to be open at the same time), then you will bleed off cylinder pressure, which equates to reduced horsepower and torque output.

On the other hand, if you’re running a high compression race motor and your camshaft has a minimal amount of overlap, the cylinder pressures can go sky high. This is far less of a problem for race engines than it is for street-bound power plants, but it should be considered and factored in at the time you choose your cam. In addition, the type of cylinder heads you’re using and the quality of available fuel should be taken into consideration. If you have to stick with pump gas, the rule of thumb is to limit compression to 10:1 with cast iron heads and 11:1 compression with aluminum heads.

I’ve had issues with bronze distributor gears in the past wearing down quickly, causing some serious ignition timing issues. What is a Melonized gear, and is it right for my small-block Chevy application?

Godbold: As most engine builder have experienced, compatibility between the distributor gear materials and the distributor drive gear on the camshaft can be an issue that can wipe out an engine if the wrong parts are selected. Melonizing was originally developed by General Motors and Ford to harden the surface of the metal through a form of nitriding and, most importantly, works great as a universal distributor gear for any camshaft application. With Melonizing, microscopic nitrogen and carbon “needles” are driven into the surface of the metal, increasing its surface hardness. The result is a lower co-efficient of friction, enhanced lubricity, and corrosion resistance.

With distributor gears, Melonizing hardens the metal, making it much less prone to wear as opposed to a bronze gear, which is not compatible with all camshaft gears. Melonized gears are available for the big three engine platforms — GM, Ford, and Chrysler — and provide amazing durability. As an added bonus, by virtue of the fact there is less distributor gear wear, more accurate ignition timing with far less spark scatter is also achieved.

What is your most popular camshaft for muscle car engine builders?

Clay: Actually, Crane has been the manufacturer of record for original blueprinted factory camshafts for a number of years. So, if you want that Duntov 30-30 camshaft, we have the original spec camshaft ready to go. We found that there were a number of customers who wanted to put their vehicles back to the original restored condition, right down to the engine internals. Nothing cries perfect restoration better than that factory thump from an original muscle car. We currently offer a long line of original engine cams for Z/28, L88, LS6, and other popular Chevy muscle cars, along with Ford big- and small-block engines, Boss 302, Boss 429, and many Mopars, from Hemis down to 340c.i. small blocks. No one has a better or more exacting replica camshafts of the factory OEM offerings.

Goldbold: COMP Cams offers a number of exact reproduction grinds made from the original OEM prints and specs. One thing that caught our attention was how well those sold even though everyone knew they might be 50-plus hp down compared to a more modern camshaft design.

Melonized Gear

Melonized distributor gears deliver long life and accurate ignition time, while avoiding the issues commonly found with excessive brass gear wear.

We started to ask our customers exactly why they wanted the reproduction cams, and their answers fell into two major categories: exact reproductions of the factory grinds or exact replication of that classic muscle car sound. For those customers looking for exact reproductions of the factory part, we already offer the perfect replacement. However, for probably the majority of customers requesting a nostalgia camshaft, they remembered a certain sound from their childhood or early years and wanted improved performance, but not at the cost of losing any of that ‘60s and ‘70 ‘personality.’

For those customers looking for that classic camshaft sound, we designed a new series of hydraulic and solid flat tappet profiles called the New Nostalgia Plus family. These profiles are slightly slower off the seat than the Xtreme Energy profiles, but have excellent area under the curve for outstanding power. The funny side effect was we started to think, ‘what if we took this a step further?’ The New Nostalgia Plus family probably helped get COMP even more excited about the sound and character of camshaft, and possibly initiated our testing of what would become the Thumpr series of camshafts, which is far more popular than either the Nostalgia or New Nostalgia Plus camshaft line.

Sources: COMP Cams, compcams.com; Crane Cams, cranecams.com

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