Updated Valvetrain Components - New Life For Tired Valvetrains
Updating A Radical, Yet Aging, Big-Block Chevy With The Latest Valvetrain Technology.
From the October, 2010 issue of Popular Hot Rodding
By Cole Quinnell
Photography by Cole Quinnell
In 1997 former President Clinton began his second term, scientists cloned Dolly the sheep, the spacecraft Pathfinder landed on Mars, and the Spice Girls released Spiceworld-their second Number One album-making the group the first British band since The Beatles to have two albums on the U.S. charts at the same time. Rock aficionados around the world mourned. That year, I was in the Bay Area, taking pictures and scribbling notes for an engine story that would appear in the August 1997 issue of Hot Rod magazine. Mike Blackstone was caressing a big-block Chevy to pump out what was some serious pump-gas horsepower for the day. Fastest street car racing was starting to get crazy and people were losing sight of the street aspect of fun, go-fast cars. This 557ci engine coming together in Blackstone's shop was designed for
both street and dragstrip duty.
After years of abuse on the...
After years of abuse on the street, this race-bred big-block Chevy developed a nasty valvetrain noise and demanded some attention. At Kurt Urban Performance, the top end of the engine was disassembled so the whole valvetrain could be inspected. This engine was built to perform really well on the dragstrip and be tolerated on the street. As such, the valvetrain required more maintenance and simply didn't last as long as a more docile setup would have.
Nearly 15 years later, the engine has seen more than a dozen dyno pulls topping out at 893 hp and 740 lb-ft of torque, countless trips down the strip with and without nitrous, and thousands of street miles, including a drive from Los Angeles to Detroit. The concessions made in favor of more power in this big brute eventually created durability issues. First, we lost a lifter driving the car through Chicago. We tossed in a new set of lifters, changed the oil, and kept driving. Within a year, though, a mystery valvetrain noise developed.
We do need to explain something about this specific engine that drove the original and the replacement valvetrain components. This was never about building a docile street engine that will deliver 50,000 miles of service by just changing the oil and spark plugs. It's not about a smooth idle or having vacuum to operate power brakes. This is about big, nasty power that scares Toyota Prius drivers when we pass them in the HOV lane. Even in our quest to replace key pieces of the valvetrain, we wanted to maintain as much of the power as possible. Our true interest was to only make compromises required for higher durability on the street. Make no mistake, these are still race-inspired designs, but thanks to nearly 15 years of technical advancements, this valvetrain should require less maintenance and deliver better endurance on the street than the
We recently took the engine to Kurt Urban Performance to tear it down and rebuild it. Urban normally builds LS engines these days, but in the early days of fastest street car racing, he built hundreds of big-block Chevys. He was very familiar with the parts we had in this engine and what the engine was built to do. We worked with COMP Cams to update the old valvetrain and solve some of the age-old problems with running a radical cam profile on the street. Quite a bit of new technology has developed for demanding applications like this. Even though this engine is on the radical side for the street, nearly all of the components are identical in function to any big-block Chevy,
and the technology is similar for any cam-in-block engine. So if you have one of these old faithful engines in your street car, there's most likely a new trick for it in this article.
The first step in any engine...
The first step in any engine upgrade should start with a thorough inspection of wear to determine what needs replacing. The mystery noise in our big-block Chevy was a damaged valve tip (arrow). The wear pattern on the other valve tips showed us that the valvetrain geometry was good. This failure was simply a matter of too many street miles on components that were engineered for racing.
This engine was built with...
This engine was built with titanium intake and exhaust valves. These are ultralightweight for high revving, and they require a little less spring pressure than a heavier stainless steel valve, however, they aren't meant for prolonged street use. Valvespring and cam profile technology has evolved so much that the 7,000 rpm that this engine spins to isn't a problem with heavier valves that will wear better on the street.
The solid roller lifters used...
The solid roller lifters used in this engine were standard race components. With this type of hardware, durability is measured in run hours. You can get quite a few trips down the dragstrip or even on a circle track compared to the run time involved in driving across the country. And most race engines get freshened up each year, which isn't necessarily true with a street engine
Why Can't These Parts Get Along?
One of the roller lifters...
One of the roller lifters had failed. Most of the time when a roller lifter breaks, the bearings have failed and the wheel locks. Once the wheel stops turning, the engine becomes a lathe, grinding down the lobe on the camshaft. Not only does this trash the cam and potentially damage the rocker arm, pushrod, and valve when excess lash is introduced, it also sends metal throughout the engine. That's what we call a bad day.
The challenge in using race-bred valvetrain parts on the street boils down to the individual parts being at odds with each other. To make maximum power, a roller camshaft snaps the valves open and closed very quickly. This places immense side-loading force on the lifters, literally forcing them up by squeezing them against their bores. In addition, the valvespring pressure is very high in order to control the valves as the cam cycles them. If the springs aren't matched to the cam profile and the maximum rpm of the engine, the valves can actually bounce when they close, and the lifters won't stay on the cam lobes. This is bad for power, and it can be catastrophic for the engine. Even with the latest technology, a huge race cam on the street will eventually kill a set of lifters. In fact, Kurt Urban recommends we replace the lifters in this engine after 5,000 street miles or immediately if we find that the valve lash loosens up. While we're at it, the valvesprings should be checked each year, and replacing them before seeing hard racing use is a wise choice. How big is too big? It's best to work with a knowledgeable team like the folks at COMP Cams to make that determination for your specific application.
Hydraulic Versus Solid
With the valvetrain completely...
With the valvetrain completely disassembled, we called COMP Cams to get the skinny on the latest valvetrain technology for these older engines. In addition to quite a few solutions for our situation, the company also just introduced some very cool die-cast aluminum, black-wrinkle big-block Chevy valve covers, and their own blend of break-in oil that address the needs of bearings and rings as well as sensitive new valvetrain components.
Most engine builders opt for more moderate cam specs on an engine that will spend most of its life on the street. Sure, you'll give up some power, but you have to weigh the pleasure of hassle-free street driving with maximum horsepower at wide-open throttle. Just as important as the cam specs is the basic type. A roller camshaft will make more power because of the steep ramps that are possible, but should you use a solid roller or hydraulic? A long time ago, a roller lifter cam meant constantly checking the valve lash-the clearance between the rocker and the valve tip. In a solid lifter setup today, that's still true. The advantage of a solid lifter, in addition to maximum power, is that the valve lash is a great canary in the coal mine. If you find more clearance, something is wearing or broken, and you need to inspect the rocker, rocker mount, valve tip, and lifter. If you suddenly have less clearance, you probably have a valve that's mushrooming, and it's time to pull the heads. Hydraulic lifters absorb some of the beating within the valvetrain, especially the bearings in the roller lifters themselves. They also alleviate having to periodically check and adjust the valve lash. Matt Summerfield at COMP really would have preferred that we use a hydraulic roller cam with 266/274 degrees of duration at .050 and .646-/.646-inch lift for this engine. This would have greatly extended the life expectancy of the lifters and would make the valvetrain virtually maintenance free.
Starting with the bumpstick,...
Starting with the bumpstick, Matt Summerfield at COMP Cams walked us through the new profiles that decrease the stress and wear on the lifters. These new profiles also require less valvespring seat pressure, which decreases stress on everything in the valvetrain. To visualize and simplify the difference in profiles, look at the old camshaft (left) that had lobes that were more rectangular in shape. This pushes the lifters sideways in their bores, literally squeezing them upward. The newer profile (right) has slightly more angle to the ramps, lowering the side-loading of the lifters. Naturally, this comes at the expense of duration, but the new profile minimizes the power loss of a "smaller" cam.
One thing that hasn't changed...
One thing that hasn't changed in roller camshaft technology is the distributor drive gear. You want to make sure you get an iron gear, which will happily mesh with a standard distributor gear. Since roller camshafts come from a race lineage, most aftermarket roller cams will require that you install a sacrificial bronze distributor gear if you don't specify an iron gear. The bronze gear on the distributor is softer than the camshaft so that it wears instead of the cam gear. This means one more thing to inspect and periodically replace if you don't have an iron gear on the cam.
The Elite Race solid roller...
The Elite Race solid roller lifters are the latest technology from COMP Cams for maximum durability in radical engines. The most significant strength improvements are a longer axle (0.400 inch) that is pinned in the body on both sides. The pins add strength, and they pressure feed oil to the axle and needle bearings. These lifters also use the highest grade roller bearings-as well as more of them-for improved load distribution. The bodies are made from 8620 steel.
You can see the top oil hole...
You can see the top oil hole (arrow) in this view. The pushrod inserts can be changed for center, left, or right offsets for custom valvetrains. The insert also features oil control that allows you to increase the volume of oil delivered to the top end in applications that need it. The Elite Race lifters are also lightweight, reducing overall valvetrain mass. The only drawback is that these lifters cost between two and three times more than others.
Another COMP Cams lifter option...
Another COMP Cams lifter option is the redesigned Endure-X. While not as trick as the Elite Race lifters, these use EDM Oil Injection, which delivers pressurized oil to the needle bearings inside the roller. This single design feature greatly improves longevity compared to standard roller lifters. Another trick is to bore a Chevy block to accept larger-diameter lifters for a Ford. The stock Chevy diameter is 0.842 inch and the Ford diameter is 0.875. The COMP Cams lifter set (PN 823-16) is designed specifically for this. COMP offers a rebuild program for the Endure-X lifters, which replaces the axle and roller assembly and inspects the rest of the lifter body.
Advancements in valvesprings...
Advancements in valvesprings over the past decade have been massive. Thirteen years ago, the valvespring required to deliver seat pressure with the valve closed was a massive triple-spring setup (right). Evolution in alloys, treatments, and coatings has allowed the use of dual springs that deliver the same control over the valvetrain. These COMP Cams valvesprings are made from Pacaloy material, which is created in a process that results in steel that is more pure. They are impact treated and the surface is chemically enhanced to remove imperfections. These steps reduce surface stress, providing greater durability.
Whenever you change valvesprings,...
Whenever you change valvesprings, there are a number of things to check. The inside of the valvesprings need to be positively located on the head; COMP Cams offers a variety of inside diameter spring seats to fit around the valveguides on the head and properly locate the springs. If you're changing the outside diameter of the spring, you'll need to change retainers too. Even if you're not, always inspect every retainer and valve lock (also called a valve keeper) for damage or wear. A failure here means a dropped valve and severe engine damage.
With extremely aggressive...
With extremely aggressive cam profiles and high spring pressures, stud-mounted rocker arms require a stud girdle for strength and stability. These are a pain, so we opted for shaft-mounted T&D rockers when we built this engine. After all this street abuse, these rockers, which were engineered for race engines, still looked and felt great. We sent them to T&D for a thorough inspection and rebuild. They inspected the aluminum bodies and steel shafts for any excessive wear and cracks. T&D replaced the needle bearing assemblies, roller tips, and 13 of the pushrod cups.
COMP Cam's nylon thrust button...
COMP Cam's nylon thrust button is a little different twist on a cam button. It's easy to cut or grind to fit but has very good wear characteristics. We really like COMP's billet keyway adjustable timing set. The double-roller chain is pre-stretched and heat-treated, the gears are machined from billet steel, and the top gear has an integrated Torrington roller thrust bearing for reduced friction and wear against the block. Degreeing the cam is easy with the nine keyway sprocket. In steps of 2 degrees, you can advance or retard the camshaft a maximum of 8 degrees.
Naturally, we replaced all...
Naturally, we replaced all of the valves. Rather than put in another set of titanium valves, we opted for a set of stainless steel valves. These are made for severe street use and should deliver years of trouble-free service. Even though these valves are quite a bit heavier, we believe that the upgrades we've made to the rest of the valvetrain will still allow us to rev the engine to its 7,000-rpm redline.