The stock W engine’s valvetrain strong and reliable enough to open and close the valves on stock engine up to 6,000 rpm, but the mechanical cam and valvesprings have a tendency to float at 6,000 rpm or more. If an owner installs bigger heads, a more aggressive cam, and a higher- flowing intake, the stock valvesprings were not stout enough to handle additional stresses placed on the valvetrain. When the valves float, catastrophic engine failure is a definite possibility. Therefore, upgrading the rocker arms, valvesprings and entire valvetrain is not only wise for a stock rebuild, but it’s an absolute necessity for a high-performance build.
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Stock Cam Timing Specs
The cam, in a certain sense, is the mechanical central processing unit of the engine. It controls the critical valve timing events that determine the engine’s powerband characteristics. As always, the engine functions as an integrated system, and there- fore, the cam must be matched to the flow capability of the heads. In addition, the heads, cam, and intake must be able to fill the combustion chamber with the maximum air/ fuel charge. As such, it is a mistake to buy large port heads, dual-quad carbs and a high-rise intake manifold and install a mild or stock cam. Like- wise, you don’t want to run a high- lift, long duration cam with stock heads and intake because top end does not give the cam enough air and fuel. And it’s all too common of a story that owner runs a cam that’s too aggressive for the street, and the car doesn’t perform strongly. While these examples may be an over simplication of the issue, it’s important to make the point.
The OEM cams were either hydraulic flat-tappet or solid-lifter camshafts. Hydraulic flat-tappet cams wear more over time, do not handle high-horsepower loads as well as roller cams, and engine oil with zinc must be used to properly lubricate them or they will wear out the cam lobes. The flat-tappet lifters produce much more friction as they follow the profile of the cam lobes. On the other hand, hydraulic or mechanical lifters have a roller tip that follows the cam profile and doesn’t wear nearly as much as the flat-tappet. In addition, flat- tappets use more duration in order to match the same amount of lift as hydraulic or solid roller cams. Flat-tappets can actually damage the lobes if the cam is too aggressive. Also, with more duration, you can experience valve overlap, causing the engine to be much more lopey and not run as cleanly at low engine speeds (RPM).
The W engines were equipped with hydraulic and solid lifter cam- shafts during its production run. Solid lifters were used as the first options for 348s with higher- lift cams and continued through the bigger and more powerful 409s. The first 409 in 1961 had 360 hp with the help of a high- lift cam and solid lifters. At the height of Chevrolet’s W- engine performance wave in 1963, there were three versions of the 409 and the smallest of these with 340 hp used hydraulic lifters; the others used solid lifters. Replacement lifters are readily avail- able for OEM W-engine lifters in both hydraulic and solid lifters. Anti-pump lifters shed their oil faster, allowing the lifter to reduce to its lowest pro- file, closing the valve faster. The trade off in these is it hurts the lift of the valve at the other end, opening it. Again, this part has a specific need and is usually used in such a manner.
All the 348s carried the hydraulic cam and the 340-hp 409s from 1963- 1965 also carried the hydraulic cam. To precisely control the valve events at higher engine speeds, all the other 409 high-performance engines carried a solid lifter camshaft. For 1961, the 409’s cam intake and exhaust lift increased to .440 inch. At 45 degrees before top dead center, the intake opens and it shuts at 92 degrees after bottom dead center. On the exhaust side, the particular exhaust valve opens at 96 degrees BBDC and shuts 25 degrees ATDC.
For 1962, the cam timing changed, the intake and exhaust valve have .480 inch of lift. At 49 degrees BTDC, the intake opens and it shuts at 93 degrees after bottom dead center. On the exhaust side, the particular exhaust valve opens at 95 degrees BBDC and shuts 45 degrees ATDC. Eventually, the race cam from the Z11 was used in the 409s. In fact, the 1964–1965 400- and 425- hp 409 engines were equipped with .557/.557 solid lifter cams.
In keeping with many of the traits of Chevrolet’s first OHV V-8, the lobe orientation on a W engine is the same as the successful small- block. The big-blocks that followed the W engines use a different lobe orientation. The camshaft bearing journal diameters of both W engines were also created the same as the small-block at 1.868 inches.
The first hydraulic 348 cams were specified at .400 inch lift and 194 degrees duration. By comparison, the bigger 409s with 425 hp used solid cams rated at .506 inch lift and 444 degrees duration.
Of course, you can rebuild your engine with an OEM Chevrolet cam- shaft, and if you’re rebuilding a W engine to strictly stock specs, then that’s an option. But cam and valve- train technology, from chromemoly pushrods to billet aluminum rocker arms, has taken such a huge leap for- ward. If you’re going to do a rebuild and enjoy the car, opt to install high- performance components. After all, no one can see inside the engine—if you’re using a hotter cam and related parts, no one is going to know it.
A myriad of cam designs, materials, and timing choices are available. The choices can seem overwhelming if you’re new to engine building. The W engine accepts hydraulic and solid flat-tappet cams, as well as hydraulic and solid roller cam- shafts. While many of the 348 and production 409 engines were fit- ted with hydraulic flat-tappet cams at the factory, the roller cams are popular options because these cams provide increased performance potential and better long-term reliability. Specifically, roller cams offer longer durations, longer service life, and the ability to support higher- horsepower loads.
Stock lifters are flat-tappet. From a performance standpoint, flat- tappet lifters are still used because they contact more of the cam lobe and do it even faster. To reduce the friction they create, numerous types of coatings have been employed to reduce the friction and drag. Many of these coatings also increase the hardness of the face of the lifter and that can contribute to longer life of the part. The name “flat-tappet” is not entirely correct as all lifters with flat bottoms are actually slightly domed to reduce friction across the face.
Flat-tappet and roller cams come in two versions—hydraulic and solid. Hydraulic lifters utilize the oil that is moving through them to essentially control the valve lash, or adjustment, of the rocker. They do this with an internal plunger and spring that move to automatically adjust the lash. Hydraulic lifters operate quieter and in the long run are more cost effective as they don’t need the many adjustments. All have their benefits and drawbacks and need to be part of the engine’s design.
Solid lifters have no self-adjusting mechanisms so their systems need manual adjustment for setting the lash. The cam manufacturer sets the specifications for lash and the adjustment is done for each valve with a size-appropriate feeler gauge and tools to loosen/tighten the fastener holding down the rocker arm. It’s pretty common to see mechanics adjusting valves at race tracks between runs. The feeler gauge is inserted between the rocker tip and end of the valve and adjusted and the rocker fastener is locked down so it will not move from that setting. Lash is often set with the engine cold during initial builds and adjusted again when the engine has been broken in and up to normal operating temperatures and clearances. By setting the lash on a hot engine, it is closer to the actual running conditions than cold. The reason for this is the expansion of hot metal and how it can affect the close tolerances and clearances of valvetrain components.
Solid lifters allow the cam’s specs to be more performance oriented. With a solid lifter, the valves can open to its full setting quicker than a hydraulic lifter. Using solid lifters can allow for more engine speed and that makes more power. With this in mind, cams are designed and dedicated to be solid or hydraulic so care should be taken to not mix hydraulic lifters on a solid cam or vice versa.
The structure of today’s cams is flat-tappet cams are cast and roller cams are machined from billet steel. On cast cams, a hardening process (such as Parkerizing) allows for better surface wear. Roller cams are usu- ally made from 8620 steel. Even the oils today’s engines use are better for roller cam use and wear.
As covered earlier, the hydraulic flat-tappet cam and valvetrain were standard equipment for most 348s and the lower-performance 409s. These lifters contain an oil chamber with a spring-loaded plunger and check valve. Oil is pumped into the lifter’s internal chamber when the lifter is resting on the base circle. The check ball prevents the oil from leaving the chamber; the pressure increases and the plunger pushes out to follow the profile of the cam lobe. The cam lobe and the lifter push the pushrod and activate the valve to open and close. The oil softens the force of the lifter, activating the pushrod and the cam provides quiet operation. These cams are suitable for a stock or slightly modified build but not extreme high-performance or racing. At high engine speeds (RPM), most lifters cannot fill and evacuate the chamber fast enough to provide consistent valve actuation, so these are not ideal for extreme high-performance or racing applications. For a slightly modified street engine and stock rebuilds, some opt for hydraulic flat-tappet cams because these are less expensive than roller cams, require less maintenance and are quieter than solid lifters. So, if you want your W engine to sound and perform like the day it did when it rolled off the assembly line and you’re not going to hot rod it, the hydraulic flat-tappet cam is the way to go. But on the down side, the lifters actually ride on the cam lobes and only a thin film of oil separates the lifters and the cam lobes so these cams cans wear faster than roller cams.
Solid Flat-Tappet Mechanical flat-tappet lifters are a step up on the performance ladder from hydraulic flat-tappets because you can run higher RPM and a more aggressive lobe profile. The solid lifter design allows the cams to operate at higher engine speed (RPM) for extended periods of time. As a result, these cams are suited for high-performance street and racing, but these are typically not selected for an extreme high-performance or race build. Unlike the hydraulic lifters, these lifters do not have an oil chamber but instead are of a solid metal design. However, they do follow the shape of the lobes and are not affected by rising temperature and fall off like hydraulic lifters. These are suited for high- performance street and some racing use. They help increase RPM and a more aggressive profile can be utilized over hydraulic flat-tappet pro- files. They usually wear quicker, must be used with a limited rev range, and need periodic valve adjustments. That’s because hydraulic lifters can’t keep up the needed valve lash at higher RPM. Solids don’t have that problem and are used in higher revving engines. Typically, a solid flat-tappet engine produces a distinctive ticking sound.
Today, the next generation of roller cams—the hydraulic roller cam—is gaining popularity. With the resurgence of the W engine, a wide range of grinds suit a variety of top end packages and applications. It still comes down to two basic styles of cams, hydraulic and solid. But the use of roller cams has increased the styles to flat-tappet hydraulic, solid flat-tap- pet, hydraulic roller and solid roller.
Hydraulic Roller Automakers are commonly using the hydraulic roller cams in performance-oriented engines. These cams are suitable for the W engine and can rev up to just under 7,000 rpm. In this design, a roller wheel on the tip of the lifter follows the profile of the cam lobe. While flat-tappet cams accelerate faster off the seat than roller cams, the roller cam sustains higher lift and duration better than a flat-tappet cam. Like hydraulic flat-tappet cams, hydraulic rollers features a lifter with an internal chamber that fills with oil to actuate the pushrod. And also similar to hydraulic flat-tappet, these cams are suitable for slightly modified engines and light-duty race use because the lifters cannot not sustain high-RPM operation.
Solid Roller The solid roller cam is the ultimate high-performance cam, and the common choice for racers searching for ultimate power. Because these require a high-grade zinc oil to live in an engine, many do not recommend these cams for a street-driven engine. Solid roller cams were originally used for primarily racing applications, but the use of solid roller cams has now migrated to the street. Solid roller cams can feature the tallest lift heights and longest durations compared to other cam types, but on the other side of the equation, these cams are louder and require more adjustment than the others. But if all out high-performance or full-on race is your application, then there is no substitute. Many owners of high-performance street cars opt for hydraulic roller cams rather than solid roller cams because the solid rollers require frequent valve lash adjustment to keep the engine in the highest state of tune.
Replacement stock lifters are readily available for W engines from a number of manufacturers. The lifters must match the type of cam. In addition, new, unseasoned metal reacts poorly when working against any that has had a chance to wear or age. The general rule in cam swaps is to buy a kit with new lifters as that is how most are sold. If a kit does not include new lifters, they can be bought separately.
Both flat-tappet hydraulic and solid lifters were OEM equipment in W engines. This means the bottom of the lifter that contacts the cam, is virtually flat and straight, providing a wide surface of contact against the cam. In actual use, flat-tappet lifters actually are ground with a slight crown on them. To match this, the lobes on a flat-tappet cam are ground with a taper, usually about .0015 to .0025 inch. Doing it this way allows the lifters to spin and avoid wear spots. By comparison, a roller lifter uses a roller to contact the cam and only the part of the roller actually touching the cam is making con- tact. With roller lifters, the contact is made more on the center of the lifter than the edges. All W-engine lifters are the same size and that is the same size as a small-block Chevy: .842 inch in diameter.
Improvements in lifters have followed cam evolution, so if you have a roller cam, you need roller lifters. Roller lifters are part solid lifter and part hydraulic. The biggest difference is the roller on the bottom of the lifter where it meets the cam lobe. Many of today’s high- performance parts use rollers at wear points to reduce friction. It’s all about having the least amount of resistance and having only the smallest part of the roller touch- ing the cam lobe, reducing drag on both parts. With less friction comes less wear, but racing parts are more about the drag than wear. Another benefit is the lack of doing any lash adjustment. Like hydraulic lifters, roller lifters need no adjustments. One area that needs to be watched on roller lifters is the roller bearing. Most roller bearings use needle bearings and like any bearing, they can break down over time.
It’s been stated before in this book, your engine works as an integrated system, and as a result, you need to select a cam that matches the rest of your engine package. In broad terms, if you build an engine with stock ported heads, stock carb, and a mid-dual-plane intake, you should select a cam with close to stock timing specs. On the other end of the spectrum, if you select high-flow aftermarket aluminum heads, dual- quad intake and large 850 cfm carbs, a high-rise intake, you should select an aggressive cam with high lift, long duration, and a wide lobe separation angle for overlap. This would produce a lot of horsepower on the top end.
When selecting a cam for your engine package, you need a cam with the right timing specs: duration and lift, lobe separation angle, advance and retard timing, and overlap. Lift is the amount of distance the valve travels from the seat, and this is the amount the lobe rises above the outside circle of the cam. A high- performance W engine cam can often produce a .0550-inch lift, and that’s what things are measured by.
Lift is directly related to the amount the valve will be moved— opening it and closing it—and rocker arm ratio also determines the amount of valve lift.
The duration of a cam is basically the time or degrees the cam affects movement of the valve. To precisely determine the actual lift of valve, you need to measure a mock-up engine with a dial indicator. Duration is measured by degrees. When select- ing a cam, the duration needed is directly related to the horsepower of the engine and the RPM it will turn. Usually, every 10 degrees of duration is good for 500–600 rpm. When choosing lift on a cam, those requirements are related to duration first.
Overlap is an important aspect of the equation, and this occurs when both the intake and exhaust valves are open at the same time around TDC. For street applications, you do not want excessive overlap, which would cause the engine to lope at idle, not pull cleanly at the lower engine speed, and harm driveability. On the other side of the coin, if you’re building an extreme high- performance or race engine, the cam must have a fair amount of overlap for the engine produce ample horse- power in the upper RPM range.
More terms in measuring a cam are lobe separation and lobe center- line angle. Lobe separation angle is the difference between the two centerlines of lobes. Using that same scenario, the lobe centerline angle, or LCA, can be determined. LCA is the angle between the two lobes. These measurements are used in determining valve overlap with a cam.
Because the W engine is a bit undervalved, the lobe centerline angle needs to be tighter, or narrower. As a rule, the more a heads flow capacity is restricted, the narrower the centerline angle needs to be. A smaller engine will have a wider LCA than a big-block engine.
Like many of the parts available today for W engines, cams and valve- trains have been upgraded by many aftermarket manufacturers. Today’s parts are better made, better per- forming, and longer lasting than ever before. The real bonus is these parts are much better designed to give you more of what you want in an engine.
Comp Cams’ hydraulic roller lifters have an advantage over flat-tappet lifters. By being designed to perform at higher engine speeds and decrease friction, they can run at higher engine speeds. They also allow for the use of more aggressive cam profiles and replace stock hydraulic and non-roller applications. (Photo Courtesy Comp Cams) Comp Cams Comp Cams is a leader in V-8 cam technology is currently offering three different grinds in the Thumpr series specifically for the W engines. These include the Thumpr for high- performance street, Mutha’ Thumpr for high-performance and street/strip, and Big Mutha’ Thumpr that’s suit- able for street/strip and race. These cams, available in hydraulic flat- tappet and hydraulic roller, provide exceptional performance and reli- ability for their specific application. Also, the cam timing provides a lopey exhaust note. The Thumpr hydraulic flat-tappet cam (48-600-5) features a 2,000 to 5,800 rpm operating range, lobe separation angle of 107 degrees F, an intake centerline of 102 degrees F. Intake duration is 278, and exhaust duration is 296. Duration at .050-inch lift is 226 on the intake side while its 241 on the exhaust side. Valve lift is .512 inch on the take and .498 inch on the exhaust.
The Mutha’ Thumpr (48-601-5) is also a hydraulic flat-tappet cam, featuring a 2,200 to 6,100 rpm operating range, lobe separation angle of 107 degrees, and an intake centerline of 102 degrees F. Intake duration is 286 while exhaust duration is 304. Duration at .050-inch lift is 234 on the intake side while its 249 on the exhaust side. Valve lift is .525 inch on the intake and .509 inch on the exhaust. In addition, Comp Cams offers several other cams that can be used with the W engines. The Comp Cams HXL solid roller cam is used frequently in many racing series. It offers .700-inch of lift, and provides 260 degrees of duration at the standard .050.
Isky supplied an RR-639/260 solid roller cam to complement the added cubic inches. Specs are .639/.639- inch lift, 294/294-degree advertised duration, 260/260-degree duration at .050 inch, and 110-degree lobe center. Hot valve lash is .028/.028 inch. Engine builder Scott Emley uses Ford Racing M-19579-A991 cam-and-lifter prelube on all surfaces because it’s super sticky and clings like mad.
When choosing between the two types of cams, hydraulic cams are often used for their benefits of less friction, lack of needed adjustments, less valvetrain noise and use of more aggressive profiles. They do, however cost more and operate in a smaller range of RPM.
Edelbrock, which has offered a myriad of W engine parts, offers a hydraulic roller camshaft called the Rollin’ Thunder. The roller cam provides a faster lift velocity and quicker valve opening and closing events so that horsepower and torque can be more readily realized. This camshaft offers steeper lift profiles for flat-tap- pet hydraulic cams, but it has sensible valve overlap to maintain low RPM performance.
The hydraulic flat-tappet cams for the 348 and 409 from Howards Cams are made of high-grade billet steel. These cams are Rockwell inspected and Parkerized for superior quality control. Howards Cams offers a stock type, several of which are high-performance street. Street/strip, and full- race cams, so the W engine builder has a wide selection of cams to suit most applications. Of course, to run these cams, piston and rod assembly and the vavletrain must be upgraded. The stock parts simply won’t handle the additional stress of a high-performance, high-lift cam, and therefore, you need to upgrade the cam along with the other top-end components, so you have a compatible and com- plementary performance package. Howards Cams offers a OEM-type hydraulic flat-tappet with .050-inch lift with 1.5:1 rocker ratio.
Like many pieces of an engine, it is commonly known a thicker- diameter pushrod can handle the load of higher lift and more aggres- sive cams and their stiffer valves- prings. Chevrolet did exactly that when they started with 5/16-inch- diameter pushrods in the 348 and increased them to 3/8 inch with the 409. The thicker pushrods gained the strength needed for the increased lift. Pushrods for intake and exhaust on Ws are different lengths with the intake pushrods being shorter. This is due to the valve placement of a W. Another change was made to the pushrods when Chevrolet updated the 409 with a new cam package. The pushrods needed to be longer to compensate for the difference of the new springs in the heads.
And as they are part of the valve- train, their length is critical in keeping the movement of the valves correct and accurate. Also like the lifters, they continue the flow of oil up into the heads. Their hollow construction acts like a pipeline and oil is pumped from the lifter up into the ends of the rocker arms. The pushrods must be strong enough for the particular valvetrain and engine setup so for a stock setup a common hardened pushrod is suit- able, but if you’re building a high-performance engine you need to select chrome-moly or stronger pushrods. In operation, the pushrods must not bend or deflect because the pushrods won’t fully activate the rocker arms and the valves if there is deflection.
If the pushrods currently installed in the engine are not straight, they must be discarded. To determine if the pushrod is straight, roll the push- rod on a piece of glass to reveal any bends. Pushrods are usually stock when they are of one-piece construc- tion with the ends shaped into balls and hardened. W-engine pushrods for intake and exhaust are different lengths, and in fact, the intake push- rods are shorter because of the valve arrangement in the head. Another change was made to the pushrods when Chevrolet updated the 409 with a new cam package. The push- rods needed to be longer to com- pensate for the difference of the new springs in the heads.
A variety of pushrods are available for stock and high-performance applications because cutting the deck and using aftermarket heads, and other modifications often require a non- stock pushrod length. Most manufac- turers, Edlebrock, Comp, and others, have sizes from 6 inches up to almost 12 inches, and sizing is done by .025- inch increments. So if a company’s catalog does not show a specific part, matching the diameter and length of the pushrod allows you to find a suit- able replacement. A growing number of aftermarket manufacturers make pushrods for W engines. Edlebrock offers case-hardened steel pushrods that are compatible with stock or Edelbrock guide plates.
Comp Cams is one of those companies that offers its pushrods more as diameter and length combinations in the hundreds it makes and sells. When checking on availability, the only information needed is the diameter and length. Crane and Comp Cams make chrome-moly pushrods for the W engines.
Comp Cams offers three different models of push rods—High Energy, Magnum, and Hi-Tech—for high- performance to race engine engines. The High Energy pushrods are for stock to mildly modified engines and exceed OEM pushrod strength. If you’re going to build an engine with more than 500 hp, you should step up to the Magnum pushrods, which are .080-inch wall chrome-moly steel tubes that are heat treated. These can cope with the stress of a high-per- formance engine up to 1,000 hp. If you’re building a full out race engine, then you should opt for the Hi-Tech pushrods, which are the strongest pushrods that Comp offers, the one- piece design has a .080-inch wall thickness and seemless tubing that is black oxide finished. Therefore, if you go beyond 1,000 hp for an all- out race build, these pushrods can handle the punishment.
The stock stamped-steel rocker arms were standard equipment on the W engine. The 348 had pressed- in rocker studs that held the 348’s rocker arms to the head while 409’s rocker arm used the same pressed- in pin, only with a drilled hole and roll pin because of the greater forces from the valvetrain. The rocker arms have a small hole in the pushrod end to collect oil until it splashes out another hole by the valvespring end to coat the springs and their caps. All W engine rocker arms, as are most of the components in the W engine val- vetrain, are very much like those of the small-block Chevy.
By comparison, the small-block Chevy uses a 1.5:1 ratio while the 348 engines used a more inclined 1.7:1 ratio and continued using those with the 409s. But that ratio is often raised when the engine is converted to solid roller cam with a 1.75:1 ratio. If you’re building a modified or high-performance or race engine, the stamped-steel rocker arms will not cope with the higher lift and additional stresses. Therefore, you must select an aftermarket rocker arm. A OEM stamped rocker arm is suitable for stock engines and slightly modified engines up to 500 hp. Above 500 hp, the stamped rocker will bend and possibly crack and fail. A high- performance engine build requires an aggressive cam, high-performance pushrods, and stiffer valvesprings, and the stock rocker arms simply cannot handle the stresses. If you’re investing in a high-performance engine build and/or changing the rocker ratio, once again, the rocker arms, preferably billet or forged, need to match the rest of the equipment in the valvetrain.
Aftermarket Rocker Arms
If your engine is using a high- lift cam, whether a solid or hydraulic cam, you need a compatible rocker arm with the right ratio that’s able to cope with the horsepower increase. The rocker arm is placed under substantial stress as it opens and closes the valves at high RPM. W-engine rocker arms are avail- able in cast, forged-steel, and billet aluminum construction. For high- horsepower applications of 600 hp or more, you should pick a forged or billet rocker arm. Your rocker choice should give the valvetrain more strength and stability so it can accurately and reliably actuate the valves. The rocker is replaced by removing the nut that holds it down, removing the old piece, and installing the new one. It then needs some adjustment depending on which type is used and needs to be retightened and the valve cover replaced. The roller rocker is one of the best types of replacement or performance rockers that provide exceptional stability and minimal wear. Most cam manufacturers offer roller rockers as a common upgrade. Talking with the manufacturer is the best way to determine what is best for your build, and they will ask about the build to help make that decision. The original W-engine ratio was 1.75:1, so, depending on the build, that is a good place to start.
Comp Cams is one manufacturer of roller rockers for 348/409 engines and Edelbrock offers them for its Performer heads. With today’s advances in metals and higher revving engines, the strength of steel is in high demand. Design and the many features of these rockers offset the weight of the metal. Comp Cams’ Ultra Pro Magnum roller rocker arms for 348/409s are constructed from 8650 chrome-moly and feature webs for increased support. These use a 3/8- inch stud diameter, 1.7:1 ratio, and have larger retainer and valvespring clearances. In addition, these fully rebuildable rockers have top-quality needle bearings and oversized trunions. These are one of the best roller rockers you can buy for the W engine.
Scorpion’s billet aluminum roller rocker arms provide exceptional strength so the rockers precisely actuate the valves and maintain the designed geometry. These pedestal- mounted CNC-machined arms are far stronger and more precise than the OEM arms. They can be rebuilt and feature a needle-bearing fulcrum and roller tip, a beefy adjusting nut, and large machined seat. Crane Cams also offers a Gold Series roller tip aluminum rocker arm in 1:7:1 ratio. Like the Comp Cams arms, these con- tain a needle-bearing fulcrum, roller tip, and extruded aluminum con- struction. These are CNC-machined aluminum alloy rockers that handle the stresses of high-performance engine operation.
If you opt for a high- performance engine build and use an aftermarket valvetrain, be aware that the aftermarket parts, in particular the rocker arms, may be taller than the stock parts and may not fit under the stock valve covers. The Z11 heads needed taller valve covers for clearance reasons. The corners of the covers did not clear the new Z11 parts so new stamped-steel valve covers were made just for that engine. If looks are not a concern in a build, a number of aftermarket valve covers are available with more clearance.
The most basic rocker-arm design is the stamped-steel type. The design originated early in the overhead-valve era and was standard issue on production small-block Chevy engines from 1955 through 1996. Only a few insignificant design changes occurred during the life of the stamped rocker. Most notably, a self-aligning version replaced the pushrod guideplate type of rockers across the board in 1987. The stamped rocker is basic, inexpensive, durable, and gets the job done. The Comp Cams Hi-Energy stamped- steel rocker arms offer a high-quality replacement for budget or stockerminded builds.
Comp Cams also offers a basic cast rocker arm with a roller tip. Called the Magnum Roller, this rocker arm uses a ball-type stud mount. The body is cast from alloy steel and heat- treated for strength, rigidity, and longevity. This rocker arm is avail- able in high-ratio versions as well.
Late-model (1987–1996) Vettes require Comp’s special narrow-body, self-aligning rockers. The narrow body allows them to fit under cen- ter-bolt valve covers, and the self- aligning tips satisfy 1987-and-up valvetrains.
The 348s started out with 1.94- inch intakes and 1.65-inch exhaust valves. When the 409 came out, the intake valves were 2.06 inches with the exhaust valves measuring 1.72 inches. One more increase in valve size came about on the popular 690 casting head when they used 2.19- inch valves on the intake and retained 1.72 inches on the exhaust. The rare Z11 used the same-size valves as the bigger 409s, with 2.19-inch intakes and 1.72-inches exhausts, but the valves were canted to perform better. Over time, the stock steel valves lose their strength, so old valves need to be replaced because they get brittle and shatter. For stock or mildly modified engines, one-piece stain- less- steel valves suffice, but for a high- performance build, you should con- sider chrome-moly multipiece valves from Edelbrock or Comp Cams.
One of the many changes in the heads was in the valvesprings. The 348 engines came with a valve- spring and dampener, and the 409s came with single springs. Later, when another more powerful 409 was introduced, it needed stronger valvesprings for the use of increased lift cams. The spring pockets cast into the heads are deeper and widened in some 409 applications for the bigger, taller spring setup. The use of higher lift cams dictated taller springs and that required more metal under the pocket to remain strong enough to support the bigger and stiffer springs.
Aftermarket valves improve an engine’s breathing, provide a more reliable component and even decrease the weight of the valvetrain. One of the more popular choices for valves is going larger in sizes. Increased valve size is a quick way to more power, but comes with a price.
When adding larger valves, it is necessary to change at least the seats to accommodate such parts. Even bigger valves would likely mean additional work on the heads themselves. Determine valve size when you’re putting together an overall build plan. Therefore, if increasing valve size for more flow, you need to have heads and intake to match the flow. Also the pistons must accommodate the increased valve size.
Big-block Chevy stainless valves are a direct drop-in once the seats are enlarged. Large 2.250-inch intake valves boost intake flow, and 454- sized 1.725-inch exhaust valves are slightly smaller but can be had off the shelf. The Chevrolet SAE report on the 348/409 says the valve heads and spark plugs were sunk into the shallow troughs solely to protect them from damage during assembly and service. The recess adds 12.2 cc to combustion-chamber volume.
The face of the valve is only one area where larger valves are built. Some companies make valves that are longer in length. Bruneau Performance Enterprises is a valvetrain specialist for W engines and uses valves that are .100 inch longer with many of their mechanical roller cam packages. The longer valves can work with higher lift cams, creating more power while keeping the valvetrain in proper geometry.
Valve material and construction are other factors to consider when going with larger valves. Stainless steel is a common material for valves but care must be taken to use the correct grade of stainless. With exhaust temperatures ranging from 900 to 1500 degrees F, separate stainless blends for intake and exhaust valves are common. Titanium offers superior strength and light weight for greater
Valvesprings, Retainers and Locks
Under most circumstances, the OEM valvesprings start to float between 5,500 and 6,000 rpm, so higher-grade retainers, locks and springs are necessary for high- performance and race builds. Today’s improvements in materials and design have greatly reduced if not eliminated that problem.
The 348 used valvesprings with dampeners and looked like two springs. When the bigger 409 was released with an intake valve size of 2.06 inches and an exhaust valve measuring 1.72 inches, then later increased again to 2.19 inches on the intake, it used taller, single springs that were a thicker diameter, a common practice from racing. With the increased spring rating, higher-lift cams could add to those 409 cubic inches, making even more power. To accommodate those taller springs, deeper pockets were cut into the heads for clearance. As the newer cams were ground with more lift, the engine needed springs that would not coil bind.
The valvesprings used in the 348/409 engines were typical for the era—a straight rate spring. The spring is uniform in wire size and the overall diameter of the spring. That kind of spring yields the same resistance as it is compressed due to its design. For high-performance and race builds, a beehive spring is often used. Bee- hive springs are also a variable rate spring offering a more complemen- tary rate to the valvetrain for opening the spring, yet a somewhat softer rate for keeping it closed or while not in motion. Variable rate valvesprings need to be matched to the rest of the components such as cam, rockers, and even the length of valves.
OEM retainers were of the umbrella design, with their shape more capping the spring than just retaining it. The reason for the umbrella design was to shroud the spring from too much oil splash. The actual piece that holds the retainer to the spring is the lock. A split-piece cap uses the steps on the valvestem to lock in place inside the inside diameter of the retainer or cap. To install the retainer and lock, the spring is compressed partially with the retainer installed over the stem of the valve. Then, the two halves of the lock are put in place around the end of the valvestem. Once the tension is reduced, the retainer moves up the stem of the valve and captures the locks in place. A valvespring compressor is used to hold the spring down so you can take the retainer and lock out of the way when removing them.
For aftermarket retainers and locks, the idea is to—much like with many of the other parts in the valve- train—reduce unsprung weight, yet provide a stable and strong system. As such, there are titanium retainers as well as aluminum and steel. For the other side of the spring, the one that rests against the head, there are valvespring locaters that isolate the steel spring with a hardened base that will not let the aluminum head wear or the spring move. Most cam manufacturers supply the needed parts for a complete valvetrain and can assist a home build in selecting parts. Even with the increased number of parts in a 348/409 valvetrain, putting one together for restoration is easy today. And in the case of racing or hot rods, W engines have many choices for improving an already strong valve- train.
Timing Chain Set
The timing chain starts all of the motion of the valvetrain. It consists of two gears, one bolted onto the camshaft and another that rides on the snout of the crankshaft. The gear bolted to the cam is twice as big as the one pressed onto the snout and that slows down the rotation of the cam. Timing gears need to be accurate or they open and close the engine’s valves at the wrong time and damage the engine. The timing chain, as it rotates the cam, is also responsible for the movement of ancillary items such as the distributor and fuel pump. The distributor rotates off a gear on the rear of the cam while an extra lobe on the front of the cam drives a shaft to actuate the mechanical fuel pump.
Factory Timing Sets
The 348 and 409 timing chain sets are the same, and Chevrolet offered no other units. As timing chain sets wear, the chain stretches and it ultimately affects the timing of the valvetrain. New units should be fairly tight with the limited deflection set at approximately 1/8 inch when properly in place on the engine. Manufacturers strongly recommend replacing the entire set should be replaced for optimum performance and to avoid the chance of having to do it all over in the future. For that reason, timing chains are usually sold only in sets with the two gears.
Aftermarket Timing Sets
Timing chains go all the way up to billet gear drives that use gears instead of chains to control and transmit motion from crankshaft to cam. In between are double roller timing chain sets, which are a good alternative to stock units for use in high- performance engines. Many different manufacturers offer stock-type timing chain sets for use in stock engine builds, and there are many high- performance aftermarket timing sets available as well. Most replacement high-performance timing gears have two more keyways in them for adjusting the timing. Using one of the two optional keyways allows the cam to be advanced or retarded +/- 2 degrees. You can advance the cam timing so the engine generates more low-end torque or retard the cam timing to generate more high- end power. This is another factor that needs to be decided upon prior to the actual build as there are many options for timing sets.
True Roller Timing Chain
True roller chain set cam gears are machined from better grades of ductile iron or hardened cast iron then heat treated after machining. Some manufacturers use billet steel for machining the crankshaft sprocket. The chains are .250 inch, full roller with side plates that are high-strength steel, and heat treated as well. The sets are hand matched for the best possible matching of gears and chain. These sets are often available for .005 and .010-inch undersize applications.
For serious high-performance and race engines, builders often eliminate the chain completely and install a gear set without a chain because gears can withstand the high-torque and stress. Installing two idler gears between the cam and crankshaft sprockets was the simple idea for what would become gear drives or, more accurately, dual- idler gear drives. Although providing provide superior reliability for high- performance and race applications, they are more known for the distinc- tive whistle they give off when run- ning that mimics the sound of the impellers of a supercharger or blower. Today, gear drives are available with and without the noise. Gear drives are usually billet steel gears that have been heat treated for durability and use two idler shafts with similar gears on them to transfer the rotation of the crankshaft to the cam sprocket. Their benefits are more accuracy and con- sistency and they are also designed to fit under stock timing chain cover.
Written by John Carollo and Posted with Permission of CarTechBooks