The line used by a CNN reporter during the early morning air attacks of Operation Iraqi Freedom in 2003 was “shock and awe” — the use of overwhelming force in the face of an enemy. As we move into the 21st century and enter the second hundred years of internal-combustion engine development, that caveman technique of using overwhelming force to control a valvetrain is quietly being replaced with what could be described as engineered finesse.
This is not to downplay the fact that high-RPM valvetrains require serious control. But, the old days of vertical-ramp cam lobes that slam valves open and slam them closed even harder are yielding to a more subtle approach to valve operation.
As an example of this approach, consider that not long ago, NHRA Pro Stock racers considered it successful if they could
coax a set of valvesprings to last more than one pass. Pushing the limits of control and RPM, these cams would sledgehammer the valvetrain against monster spring loads in an attempt to maintain control over the valves.
COMP’s Valvetrain Engineering Group Manager Billy Godbold and his team have been flogging valvetrains for years in a search for the next breakthrough in valvetrain technology. Recent advancements in testing have led to what COMP now calls Low Shock Technology.
Taming the Bull In the China Shop
Since the beginnings of the internal combustion engine, the limitations of making power have revolved around the challenges of achieving reliable higher engine speeds. Once Bob Fox designed and produced the first Spintron machine, that tool made a major pivotal step toward reliable valvetrain testing.
That machine uses a hefty electric motor to drive a crankshaft in a cylinder block to spin a valvetrain at anywhere from idle up to ludicrous engine speeds. While this whirling dervish is making incredible noise at 11,000 rpm, the machine is also using a laser to precisely monitor the valve position. The goal of these noisy exercises is to ensure the valve accurately follows the cam lobe’s intended profile. The execution of that plan is far more difficult than it may appear.
EngineLabs readers may be familiar with one of the more-celebrated examples of this high-RPM development – the 427ci LS engine program dubbed Project Spinal Tap. Pushed along by its creator and progenitor Ben Strader of EFI University, the Spinal Tap engine was designed to achieve repeatable and survivable forays into the 11,000 rpm engine speed stratosphere. It did this quite nicely, thank you.
The Spinal Tap engine valvetrain was developed with guidance and direction from Godbold, along with EFI University. Together, they worked on a systems approach to controlling these spurious accelerations that always seem to afflict high-RPM pushrod valvetrains.
What we’ll focus on here are a couple of technical nuggets gleaned from this development process as they relate to the camshaft lobe shape, as they eventually became COMP Cams’ new line of Low Shock Technology (LST) lobes.
The real difference is that by loading the system a bit more softly in the very, very early stages, we can push it harder, later in the opening. — Billy Godbold, COMP Cams
Testing With Lasers
Ben Strader shared three of his Spintron reports with us. These reports can put into simple pictures what would otherwise take literal reams of complex descriptions to explain. Trace 1 is a baseline cam lobe at 3,500 rpm. The upper portion of the graph shows the engine speed as a slope running from 0 to 3,500 rpm.
The lower half shows two traces. The green trace is the valve lift curve (which should be self-explanatory). The second brown trace is valve acceleration (both positive and negative) expressed as a change in velocity-per-degree of lobe movement.
The high positive acceleration on the left side of the trace reveals hard valve acceleration as it lifts off the seat. The valve then decelerates as it runs across peak lift. Note also how the acceleration flattens out as the valve approaches the seat on the closing side. This indicates a stable valvetrain that is delivering an accurate lift curve.
Now let’s move to Trace 2, which is this same lobe at 9,500 rpm Note first, this test overlays the 3,500 rpm green lift curve with a yellow trace. Also, note how the yellow trace loses lift on the opening side of the curve and then increases lift on the closing side. This reduced lift on the opening side is system deflection that is delivered back into the system on the closing side much like a pole vaulter’s pole bends and then straightens as he approaches the crossbar.
The most important red flag in Trace 2 is the 0.020-inch bump after valve closing. This is where the valve actually bounces off the seat and stays open for roughly another 45 crankshaft degrees. At this point, the valvetrain has aggressively entered the Twilight Zone of valve-float where power drops off precipitously because the intake valve is not closed. The cylinder can’t begin to make pressure until the valve closes and is the cause of power dropping off so badly at high-RPM.
Looking at the brown valve-acceleration curve, you can see how badly it fluctuates in the center part of the curve through peak lift. Note there are two serious spikes in acceleration during this period that should not be there. This indicates bad things are happening to the valvespring.
Smoothing Out the Curve
Now we get to the good part. Trace 3 employs similar cam-timing figures as far as opening and closing points, but employs Low Shock Technology to reveal the stability at a similarly-high 9,582 rpm. Look at how stable the yellow lift curve is and how close it approximates the green curve from Trace 1.
There is still deflection, but it is stable. Plus, note how acceleration (brown line) reveals reduced amplitude of the acceleration spikes across the peak lift (middle) portion of the curve. Additionally, there is only a slight hint of valve-bounce on valve closing.
In typical Godbold fashion, he has taken what is a very complex set of parameters and simplified it into an easy-to-digest explanation, saying, “The peak accelerations on the new Low Shock lobes are quite similar to our older LS-R designs. The real difference is that by loading the system a bit more softly in the very, very early stages, we can push it harder, later in the opening. And more yet on the closing, because the spring is not all ticked-off and surging like Jell-O on a shaker table.”
That Jell-O reference is a great mental picture of what the valvespring looks like when it’s in distress. If you’ve ever watched one of those ultra-slow motion videos of a valvespring doing The Watusi at high engine speeds — those are dynamic valvetrain forces at work. The dynamic forces are enormous, often several magnitudes greater than static measurements of open spring load.
What Godbold is saying here, is that by not hammering the valvespring at the early opening points on the lobe, this gentler acceleration rate lowers the stresses absorbed by the valvespring in these same moments. By doing this, the valvespring retains control over the valve over the entire valve-lift curve, and as a result, can handle a higher RPM range.
Godbold followed-up his statement by adding, “The [valve] accelerations may ultimately be higher than the older designs.” These valve accelerations later in the lift curve will open the valve quicker, hold it open longer, and close it quicker compared to older lobe designs.
This can lead to improved power being made by virtue of a more stable valvetrain. All of these improvements occur within very similar cam specs. That is why merely looking at the duration, or even valve opening and closing points, will not tell you how well a cam will work.
Example LST Camshaft Specs
|CAMSHAFT||ADVERTISED DURATION||DURATION AT .050″||VALVE LIFT (INCHES)||LSA|
|LST Hyd. Roller|
|HRT Stage 3|
|LST Mech. Roller|
It Takes a Village
Exerting improved dynamic control is not attained solely by massaging the opening and closing accelerations of the lobe, although that is the key factor. Any discussion of improved valve control must also acknowledge how the rest of the valvetrain assists in this program. This includes lifters, pushrods, rocker arms, retainers, and locks. While you can order an LST camshaft for an LS3 by itself, the intelligent route is to consider Comp’s camshaft kit (CK) that includes all of those matched components, except the rocker arms.
Control isn’t simply a matter of jacking up the spring rate and calling it a success. After many hours of Spintron testing, COMP has complemented the GM LS engine LST lobes with a dual valvespring package. Even within the tight confines of the LS engine’s stock spring pad, the dual springs offer significant valve control advantages.
COMP has developed a series of packages for the LST design that encompasses a Stage 1 and more aggressive Stage 2 version for a wide range of LS engines in both hydraulic-roller and mechanical-roller renditions. The engine families include the 6.2L LS3, 2014 and newer LT1 engines, as well as 4.8L and 5.3L truck-style turbo applications. On the mechanical-roller side of things, there are a couple of big solid-roller versions capable of handling valve-lift approaching 0.675-inch.
Of course, the impressive Mopar late-model Hemis will also benefit from this technology. COMP calls these the HRT packages. Using this same cam lobe approach, Comp has created Stage 1, Stage 2, and even Stage 3 packages for engines like the 2003-’08 5.7L Hemis, the 2009-and-later versions, and of course the 2011-and-newer 6.4L. Like the GM engines, each of these cam packages are matched with components that have been Spintron-tested to work together.
Interestingly, the Stage 1 version of the HRT packages are designated as NSR cams, which stands for No Spring Required, meaning that with the milder Stage 1 cam, you can retain the engine’s stock valvesprings. But to take maximum advantage of the potential gains with Stage 2 and 3 cams, these will require spring changes.
We will follow this story up with a dyno test comparison of a new Low Shock Technology cam versus an older lobe shape, along with the entire LST cam kit assembly. It should be interesting. Stay tuned.