In a world without limits, camshaft designers have known for decades what profiles they'd like to grind. But real-world technological limitations-in terms of design feasibility, materials science, and manufacturing process-have held them back. Now, the introduction of sophisticated lobe design and analysis software, better materials, and computer-controlled manufacturing has pushed cams and lifters into a whole new performance envelope. Then there's recent original-equipment innovations such as variable valve timing (VVT) and perhaps ultimately electronic valve timing. There's no telling where it will all end. From the lowest street cam to the most radical high-end professional racing applications, big changes are occurring, so HOT ROD felt it was high-time we took a look at the state of today's cam and lifter technology.
It's a Digital World
Today progressive cam companies design all their new profiles on a computer, then use engine simulation software to analyze a new design's projected performance. As Isky Cams' Nolan Jamora puts it, "The time and money that these design programs save us is immeasurable. To be able to work out what could be initial problems inherent in pushing cam and valvetrain design to the next step has proved invaluable. To simulate how a particular design will react to different valvetrain materials and evaluate the Hertzian stresses imparted on each part has allowed us to optimize each individual component in the valvetrain."
Profiles For Success
All the analysis and testing have yielded big refinements in overall lobe profile shape. The new-tech lobes are asymmetrical, with different opening and closing shapes. Single-pattern cams with identical intake and exhaust lobes are yesterday's news. Today the trend is toward dual-pattern designs with dedicated intake and exhaust lobe shapes that vary beyond mere lift and duration differences. "Racers and engine builders are looking at durations beyond the 0.050-inch number," says Kevin Cantrell at Schneider Racing Cams. "They want to know what the duration is at the lash point, at the 0.200 mark, and so on."
On the intake side, the goal is to yank the intake valve off the seat and accelerate it over the nose as quickly as possible, all while smoothly following the intended lobe profile shape. This gets the valve well up into the max flow range of today's high-flowing cylinder heads as quickly as possible for a given rpm window. Avoiding destabilizing valve bounce mandates the closing side be made smoother and gentler, especially as the valve approaches the seat.
"The old rule of thumb on the exhaust side was to just make sure you did not choose something that would hurt performance," says Comp Cams' Billy Godbold. "Many of the common exhaust lobes were either leftover intake designs or quite lazy cam profiles that seemed to take days to get the valve off and back on the seat." Now new exhaust-specific designs are being introduced that are definitely not "soft." These are still slightly softer right at the seat than the newest intake designs, but the entire curve is no longer soft, yielding more area under the curve. Collectively, this reduces exhaust pumping losses and yields a much flatter torque curve while still minimizing valve breakage and premature exhaust seat wear. The new-theory dual pattern optimizes the overlap triangle shape, helping the headers do their job of providing a low-pressure signal back to the inlet charge.
According to Schneider Cams, there are, however, some cases where really old-school lobes are making a comeback. "We have actually been using some of our original racing profiles designed in the early '60s again because they are still really good profiles. But back when we first designed them we did not have valve-springs good enough to control their fast ramps. Now we do."
The refinement in design, materials, and manufacturing isn't just for racers. Today's street cars run so much better than 10 or 20 years ago because the heads are much better, the valvetrains are more reliable, and the aggressive, computer-optimized lobe profiles really work (and live). Don't believe it? Look how much more power GM's LS series, Chrysler's Hemi, and the Ford Modular series make in stock form (let alone with a simple cam change), compared with the designs they replaced.
For computer-controlled, fuel-injected engines, cam designers are trying to come up with bigger 0.050 durations that are still computer compatible. Mid-220s duration used to be the benchmark, but for the most part that can now be stretched to at least the mid-230s with lobe-separation angles of 110 degrees or greater (assuming a stock computer reflash or an aftermarket self-learning or reprogrammable system). "For the most part, we can now make the cam move the most air in the cylinder as possible for a given induction system and rpm and expect that any good tuner will be able to get the idle and air/fuel ratios correct," Godbold says. "However, because cylinder heads are also better, it has come full circle, so that often you don't need any more than 224 degrees at 0.050 for most LS street EFI applications." But if you did want to go big, mechanically it's easier than ever: Many factory-performance versions of today's engine families feature lightweight valves, while on the aftermarket side there are 0.675-inch-lift-capable valvesprings available that fit in the stock pockets.
For carbureted applications on old-school hot rod motors, Comp's Thumpr series cams are proving popular, and not just because they sound good, like a camshaft should. They are also more filling, with a very wide power curve, perhaps the most important attribute for a street cam. Yet the designs are quite stable at high rpm. At the same time, the tight 107-degree lobe separation and shorter intake duration result in an early intake closing to help trap the charge at low rpm, yielding a strong torque peak at a moderate rpm. Thumprs have been so successful that they're even available for oddball motors like nailhead Buicks, early Hemis, and flathead and Y-block Fords. Other quick-acting, broadband street cam series include Lunati's Voodoo, Isky's HRX and Fat Hydraulic grinds, and Crane's Energizer series.
The Quest For Stability
At the high end, racers have always wanted quicker cams, higher lift cams, and longer duration. But to realize the full benefits of a quick, high-lift cam requires a stable valvetrain. As Chase Knight at Crane Cams puts it, "Anytime you can get the valve to do what the cam signals it to do repeatedly, you've made significant gains." Initially, huge lift was generated by upping the 1.5:1 to 1.7:1 rocker ratios common 10 to 15 years ago to as high as 2:1. This first occurred in NASCAR where flat-tappets are mandatory, but eventually spread to roller-cam apps as well. Unfortunately, the higher the rocker ratio, the more the force multiplication on the tappet side of the pushrod: With a 2,000-pound inertial load, the load on the pushrod side is 3,000 pounds with a 1.5:1 ratio but 4,000 pounds with a 2:1 ratio. Even though pushrods got stiffer (Pro Stock diameters are more than 1/2 inch, and some Top Fuelers even use solid pushrods), shaft-mount rocker arms replaced stud-mounted independent rockers, and vastly improved valvesprings became available, it still wasn't enough to prevent valvetrain flex. The problems weren't just confined to Pro Stockers and Fuelers. "Even Super Stock Hemi guys running 800 pounds on the seat and 1,200 pounds open with 1.875:1 rocker ratios at 9,500 rpm had this problem," says valvetrain expert Dan Jesel. "People didn't realize how bad their pieces were until they got a Spintron," Knight adds.
Today most roller follower applications are moving back toward the 1.8:1 range or lower, yet net valve lift is holding steady or even increasing. The difference is made up by increasing lobe lift-in pro racing, lobe lifts sometimes approach the low- to mid-0.600s with even some bracket racers running up to 0.515 inch. Alternatively, Crane posits the new, more stable valvetrain "enables you to have a milder cam profile in general because it transmits the lobe profile more accurately. You can see 30 hp on a single-four-barrel, 7,500-rpm engine because shorter seat timing (but better cylinder filling) ends up broadening the power curve."
Of course, the taller lobes have to physically fit through the block's cam journals. Traditionally, a cam's base circle diameter was reduced to permit higher-lift lobes to clear. But a thinner cam core twists and flexes. "Cam bending is a primary cause of mysterious piston-to-valve problems," maintains Jesel. "I've wanted big cams forever." With new specialty aftermarket engine blocks that accept larger cam journals supported by needle-roller cam bearings, Jesel can finally have them.
Even relatively thin needle cam bearings take up some space, reducing the amount of ultimate clearance available. Jesel is said to be working on new clamshell hydrostatic bearing technology and revised lubrication "that oils the cam down the middle." If successful, it could permit even larger cam cores than at present, or make practical installing relatively larger cams into stock-style blocks.
But, it does little good to put a large journal on a cam if the lobes no longer clear the connecting rods-so many of the new blocks also have the cam centerline raised for more rod clearance. This dovetails nicely with the increased use of big stroker kits. For example, the new RHS LS race block moved the cam up by the equivalent of two timing chain links and added a 60mm cam journal, permitting a fullsize base circle even with a 4.600-inch stroke.
Concomitant with larger cam cores has been a proliferation of different cores custom-tailored for specific applications. With all the different aftermarket heads out there, valve locations and angles and even optimum lifter bore positioning has departed from the original factory designs. To keep the lifter and pushrod as straight as possible, the lobes on the new cores are reclocked and repositioned so the lifters track down the center of each lobe.
There have also been changes in materials and heat-treating processes to increase cam life and load-bearing performance. Jesel has continued to refine its proprietary H-13 aerospace steel raw billets for custom race cam grinding. While expensive, the tool-steel blanks are hardened completely through the core. So are many Comp Cams rollers and high-end NASCAR flat-tappet grinds that are now made from Carpenter powdered-metal tool-steel billets. The powder isn't put into a mold and heated like cheap OE connecting rods; instead, a very fine powder matrix is used to make the base material resulting in what Comp terms truly "out of this world" improvements in "wear resistance, strength, and toughness."
With evermore lift and duration (and thus ever-higher valve-spring pressures), solid roller lifters have a large load to bear. As Isky puts it, "Extensive testing confirmed rather than being continuous and orderly, needle-roller motion in the roller bearing is subject to harmonic wave-like action that oscillates between the bunching up and spreading apart of the needles, due primarily to deflection of the outer bearing race under extremely heavy valvespring loads and tremendous dynamic forces. This was exacerbated by the poor load distribution ratio of surface area contact of the needle rollers." If you ever had a roller lifter come apart at 8,000 rpm, the results are not pretty.
One solution is beefing up the roller axle and increasing needle-bearing quality, size, and number, but with a production-based block you run into the physical packaging constraints of the roller lifter assembly versus the lifter-bore size of engine families designed a half century ago. One solution is special aftermarket blocks designed to support much larger lifter body sizes made from premium materials.
Oversize lifters, special cylinder blocks, and extra machining are costly, so Isky has gone a completely different route to improve durability while keeping costs under control. After years of experimentation with different materials and manufacturing processes, it's developed the EZ Roll Red Zone needleless, single roller bushing design that replaces the roller needles. Isky claims "they last four times longer, and love high heat and low oil, making them perfect even for a street car idling in traffic."
Have Lifter, Won't Travel
We've seen that a major quest for improving cam performance is making the entire system more stable. As Comp puts it, "Deflection always increases with load and load increases with rpm." It's more of a problem with a hydraulic tappet compared with a solid because of the traditional hydraulic lifter's long plunger travel. As rpm increase on an overhead-valve engine, this can decrease running valve duration by as much as 10 degrees. The problem was especially acute with hydraulic rollers, which some believe never achieved their full top-end potential.
Short of converting to solid roller lifters, one approach is raising spring rates to near solid roller cam levels, then install lightweight valves, stout pushrods, and beefy rocker arms. Crane has hydraulic rollers running with 240-to-250-pound seat pressures in big-block Chevy-powered Navy SEAL attack boats that obviously have to work right all the time. At the drags, Crane says hydraulic rollers set up with big springs are drastically reducing pesky between-rounds maintenance on some Super Gas and Super Comp cars. On the other hand, for daily street use, upping hydraulic roller spring pressures shortens lifter life, plus the lifters tended to bleed-down from all the pressure overnight, leading to noisy cold-starts.
The problem is also being attacked at its source by improving the lifter design. The limited-production ZR1 Corvettes wind up high using special GM lightweight lifters that substitute a lightweight ceramic check ball in place of the normal steel one. In the aftermarket, Comp Cams has come up with short-travel lifters, which it maintains come closer to the performance of a solid roller than anything else previously available.
The new short-travel lifters achieve their maximum capability with Comp's new hybrid hydraulic roller lobes. In years past, a primary concern of every hydraulic roller design was limiting lifter noise at idle. However, some of the best race hydraulic roller lobes were actually older tight-lash solid roller profiles. "This sent us back to the drawing board," admits Comp. "It has resulted in several new lobe series that are partly what looks like a solid roller acceleration curve and partly like a hydraulic roller design." These new lobe families can either be run with a short-travel hydraulic roller or a tightly lashed solid roller. In an LS application, using a short-travel hydraulic roller lifter and a Comp PN 26926 valvespring, Comp tested a 0.675-inch-lift hybrid lobe up to 7,500 rpm without control loss. Currently, these are only offered as customs because many end users may have issues with the additional noise.
Phasers On Kill
Beyond cam profile improvements, there is variable valve timing. Used stock on some late-model engines, it's most commonly implemented as a way to automatically ad-vance and retard the camshaft under running conditions. A computer-controlled, hydraulically driven, phaser mechanism installed in place of the standard cam sprocket is used to accomplish this function. In production, VVT mainly improves fuel economy and emissions, but for hot rod use it has the potential to broaden the power and torque curves, once two potential problems are overcome: First, piston-to-valve contact will occur with a big cam because the preprogrammed stock advance and retard range is too broad; and second, the phaser mechanism may have insufficient hydraulic pressure to overcome high-pressure valvesprings.
Short of an engine rebuild with deeply notched pistons, the contact problem can be managed by reprogramming the factory computer to electronically limit phaser advance and retard or by mechanically restricting phaser movement with a hardware-derived phaser limitation system. As tested on a GM L92 6.2L LS engine, a Comp Cams phaser limiter kit made 500 hp (gaining 70 hp over the stock 430hp baseline), with no losses anywhere compared with the stock cam. Meanwhile, new valvespring designs are in the pipeline that provide sufficient cam control without overcoming the phaser mechanism.
One company that offers cams that retain the full VVT function is Mast Motorsports.
Due to cost and complexity, we're not likely to see VVT retrofit kits for old-school engines any time soon. And full-race engines are unlikely to benefit from advance/retard VVT tech because they run in a very narrow rpm window. There are various VVT systems that can change the lobe-separation angle as well as cam advance, such as the Dodge Viper V-12 "cam-in-cam" system for pushrod engines and various import OHC configurations. These could have serious race potential, if a similar setup were ever implemented on mainstream engines.
A Farewell To Cams?
VVT aside, in the future, physical cams could be entirely replaced by electronic valve actuation systems. These systems exist today, but they're only for very low-lift and low-rpm diesel engines because present electronic solenoid technology eats power and doesn't work well over 0.400-inch lift and 3,000 rpm. They're bound to improve in the future, though. At the very least, we could see the perfection of air-springs (some Formula I cars already use them). However the valves are actuated, there will still be a need for a profiler. "We look at ourselves as designing valve motion," says Lunati's Derek Scott. "So in this sense our job will stay the same-we just might be programming chips instead of grinding eccentrics on a metallic shaft."
One thing's for sure: Every year, new developments help push engine performance higher, cars go faster, and new records are set. These are no longer the days of your granddad's 30-30 cam.
Taps For Flat-Tappets?
The rash of flat-tappet cam failures a few years back is attributed to manufacturing defects in the lifters themselves, a change in the composition of commonly available motor oils, and (in some cases) worn lifter bores that reduced the amount of normal flat-tappet lifter-crown rotation. With modern engines no longer using roller lifters, traditional U.S.-made lifter sources dried up, and poorly made foreign lifters flooded the market. This has since been corrected, and the major cam companies have assured us that all lifters sold by them are made in the U.S.A. by reputable companies. Cam companies have also improved their flat-tappet cam heat-treat process and quality-control procedures. For example, Isky uses only U.S.A.-made cam cores. Both Bullet and Isky stress the need for additional taper on the lifters and the cam lobes.
That still leaves the oil. Zinc dithiophosphate (ZDP), an antiwear/oxidation inhibitor chemical additive, was once used in motor oils to act, Schneider Cams says, "as a high-pressure lubricant that is crucial to lobe/tappet life when using a slider-type lifter." With today's engines all running rollers, ZDP was removed from street-car oils for emissions-control reasons. Although mild, stock, flat-tappet cams generally don't encounter problems, aftermarket hot rod grinds are much more aggressive and cannot rely on current passenger-car motor oils for adequate protection.
The obvious solution, says Crane, "is not to run a flat-tappet unless the rules mandate it or you can't afford a roller." Besides, Schneider points out that "roller cams increase power by as much as 10 percent over a flat-tappet with comparable specifications." Unfortunately, "racing promoters that require flat-tappet cams won't be changing any time soon," maintains Bullet Cams' John Partridge. "They think they are saving money when in fact they are costing them money." The exotic-material NASCAR cam billets, lifters, and coatings cost around $5,000 a set and last for three races if the engine builder gets lucky. A roller cam and lifters would be four to five times less costly.