It's appropriate, we think, that a camshaft has lobes, since this relatively simple device is so often called the brains of an engine. And indeed, a camshaft does direct several engine functions in a brainlike manner, controlling when an engine's valves open, how long they stay open, and when they shut--thus determining how much power that engine makes. On the other hand, the arrangement of the cam's lobes gives an engine its personality, influencing what type of power it will make and where it will come on in the rpm range. The camshaft may be the brain of an internal combustion powerplant, but for performance enthusiasts, it's also the heart and soul, giving our engines their very character. When properly matched to the other components to meet a specific goal, a camshaft can create an engine that's a dream to live with. A poorly chosen cam, on the other hand, can create an ill-tempered, underperforming beast.
Notice that when we talk about the right cam, we're talking about the right cam for your combination. A multitude of variables must be taken into account when selecting a camshaft. Engine displacement is a biggie, so to speak, but so is engine compression. "You have to have a suitable compression ratio for what you're doing," says Crane Cams' Chase Knight. Too little compression ratio--or too much duration--can lead to a drop in cylinder pressure and a corresponding drop in power. Too much compression--or too little duration--can create too much cylinder pressure, leading to detonation. Both are bad, and good reasons to follow the cam maker's compression ratio guidelines. Other factors to account for include the type of cylinder heads, the intake manifold design, and the carb size. Then again, you can't drive an engine by itself, which brings in a whole new group of variables: car weight, transmission type, torque converter stall speed if running an automatic, and rearend ratio. It's a lot to consider.
But the biggest considerations are honesty about your purposes and the setting of realistic goals. "When it comes to what camshaft you need, you have to ask, `What are you trying to make?'" opines Comp's Billy Godbold. "With really excellent cars, I guarantee you, there was a plan that was followed." So what's your plan, and is it reasonable? Lots of high-rpm horsepower sounds good, but how often will you actually rev the engine to 7,000 rpm to get that power? Are you planning to go racing on a regular basis, or do you actually fall more on the street side of the street/strip equation? Possibly you want a ride that can handle the Hot Rod Power Tour...or do you really just need a little extra something in a daily driver?
Whatever your goals are, be honest with yourself--if you're not, chances are you're not gonna be pleased once that new 'stick is in place. "Guys pick a cam, we advise against it, they end up calling back," says Knight, the implication being that the customers aren't happy when they make that second phone call. In the end, it's all about creating a power curve you can use, with power happening where you actually drive the car. "To me, torque is what makes everything fun, especially when you can smoke the tires at 3,000 rpm," says Knight. It's a good point, and harder to do if your peak torque happens at 5,000 rpm. On the other hand, if you are going racing, and can actually use high-rpm power, cam accordingly. "Buy a cam for the car you have, and not for the car you want," says Godbold, a piece of wisdom echoed by all our experts.
Once you've taken inventory of your particular combination and your goals for it, you're ready to go shopping. "Be honest with your cam company," says Knight. "You'll get a better overall combination." And that's what it's all about, of course, and as we've pointed out, a poor combination can make your life miserable. The camshaft is critical to producing the type of power you're looking for, but only when properly matched to the rest of your components. "The performance you can get from having the right engine combo is better than it's ever been," says Godbold. "And the reason we make so much power is that everything is tuned together." That's the goal we all have--cam companies included. Read on, and good luck in creating a combo you can really live with.
Everybody has cars and combos that need a cam. They're now running good enough stuff where new cam technology would be a benefit.
--Nolan Jamora, Isky Racing Cams
What we did
Examined the factors in selecting a performance camshaft
Picking a cam that matches your goals and your engine combo is crucial for performance and enjoyment.
From $100 for a hydraulic flat-tappet to $700 for a hydraulic roller
It's usually the first choice made when swapping cams, and there are four options to choose from: hydraulic flat-tappet, hydraulic roller, solid flat-tappet, and solid roller. We've listed the types in order of increasing power potential, but each has advantages and disadvantages. A roller cam's greatest benefit is that its frictional forces are less than those created by the sliding action of a flat-tappet cam, which frees up some horsepower. Another advantage is that, for the most part, roller profiles can be more aggressive, employing more lift given a particular duration. On the other hand, a flat-tappet cam actually has greater initial acceleration, meaning it will attain higher lift more quickly than a roller cam, before the roller reaches its maximum velocity--which means running a flat-tappet setup can actually be the better choice when running a cam with short duration figures. As we've said throughout, it's all about choosing what works best with your combo to meet your goals.
They're inexpensive, they don't require any adjustment since engine oil pressure maintains preload against the pushrod, via a spring-loaded plunger, and they run quieter than mechanical lifters. On the other hand, they often perform poorly at higher rpm due to an inability to bleed down excessive oil pressure.
This type of tappet has been used in OEM small-blocks for the past 20 years. The roller design allows for more aggressive lobe profiles, along with the self adjustability and quiet operation of hydraulic lifters. These lifters are constantly improved but can also suffer from high-rpm limitations. In general, these cams are the most expensive, especially when springing for a retrofit cam and lifter set for an older block.
Also called a solid tappet, since it provides a solid link between the cam lobe and the pushrod, this is about as basic as it gets and is only slightly more expensive than a hydraulic flat-tappet system. These cams will rev higher than hydraulic cams but tend to be noisier. They also require a valve lash setting to account for expansion as the engine heats up.
The best of both worlds, this type of lifter allows for the more aggressive lobe designs of a roller setup along with high-rpm operation, thanks to its solid body design. It also requires a lash setting that must be periodically readjusted. A retrofit mechanical roller costs less than a similar hydraulic setup but is still quite a bit more expensive than a flat-tappet arrangement.
According to Knight, you can compare similar hydraulic and solid cams by using an 8-degree cross-reference figure. For example, a hydraulic cam with 222 degrees duration at 0.050 equals a solid cam with 230 degrees duration at 0.050.
Selecting what type of cam to use may be the first decision usually made, but choosing the cam's duration figures--the amount of time the valves are held open--is arguably the most important. "Duration and lobe separation pretty much control the engine's basic rpm range," says Knight. "Lift controls how much power you make in that rpm range."
That being said, we'll tackle duration here and consider the other two elsewhere. In general, shorter-duration camshafts produce power lower in the rpm range and lend themselves toward a smooth idle and good part-throttle response. Longer-duration cams produce their power at a higher rpm but sacrifice lower-end grunt as the powerband is moved up. So what constitutes shorter and longer duration, at least when it comes to a traditional small-block Chevy? "The lower 200s to 220 degree range (measured at 0.050) is more street-performance oriented," says Lunati's James Humphrey. "Once you're in the 230-250 degree range, you're getting into more of a street/strip application." At this level, the powerband comes in later, after 2,500 rpm, and if you're running an automatic transmission, you'll need a converter with a higher-than-stock stall speed. Once you're running duration longer than 250 degrees at 0.050, according to Humphrey, you're dealing with a hi-po setup more suited to the track than the street.
It's also important to remember that increasing duration without changing the cam's lobe separation angle increases overlap, which also furthers high-rpm performance at the expense of low-end grunt. So what duration level is right for you? Again, it depends on what you're trying to accomplish with the combination you have. "A guy in a street car sees more benefit in torque," observes Humphrey. "That's what carries a guy." But as with most things, choosing duration is a compromise, and leaning toward the conservative side with this spec helps create a wider, user-friendly torque band.
According to Crane, each 10-degree change in duration causes the engine's powerband to move up or down approximately 500 rpm.
LOBE SEPARATION ANGLE EFFECTS
Increased low-rpm torque
Reduced idle quality
Increased cranking compression
Decreased piston-to-valve clearance
Improved top-end power
Improved idle quality
Reduced cranking comparession
Increased piston-to-valve clearance
It's one thing to talk about cam specs and throw out terms like "area under the curve," and quite another to see those plotted out on a graph. Note the difference between advertised duration and duration at 0.050. Remember, it takes two turns of the camshaft (720 degrees) to complete the four-stroke cycle for every one crankshaft turn.
Flat-tappet cams work well in many applications, but they create much more friction than their roller brethren. And as shown here, flat-tappet profiles can only be so aggressive before reaching their limits. This diagram also illustrates why flat-tappet lifters can't be reused when installing a new cam, since the two mate during break-in. Roller cams create much less friction and can reach higher velocities, allowing for more aggressive profiles that can achieve higher lift levels within a given duration.
Camshafts only look simple; in reality, they're complex devices that control all four valve events (intake open, intake close, exhaust open, exhaust close), as well as how far the valve opens, how long they stay open, and how long they're both open at the same time. These factors, along with the distance between the intake and exhaust centerlines (LSA), determine how much power an engine will make and where in the rpm range it will make it.
In most cases, the benefits of running a roller cam are hard to argue with, since it can achieve higher velocities than a flat-tappet cam with the same amount of lift. This creates more area under the curve, which translates to improved power at lower valve lifts. On the other hand, a flat-tappet cam's initial acceleration is faster so it actually achieves higher lift levels more quickly than a roller cam until the latter reaches its maximum velocity. If you're running a short-duration cam, a flat-tappet lifter may actually be the better choice.
In general, increasing valve lift allows more air/fuel mixture to enter the cylinders and more exhaust to exit, which leads to an increase in engine performance--but only to a certain extent. The first thing to consider is the cylinder heads you're using. "You want to try and utilize your heads as much as possible," says Humphrey. Accordingly, you should always try to get your hand on flow figures for your lungs of choice when selecting a camshaft. On the other hand, there's no point in adding lift when it can't be used. This is especially true considering that an increase in lift almost always leads to at least a slight increase in duration, since the cam needs longer opening and closing ramps to accommodate the extra lift. This increased duration is not always good, since it can alter the engine's powerband. Modern, computer-aided cam design, however, lessens this effect by enabling designers to create more complex and efficient lobe designs that aim for lots of high-lift duration without low-lift duration... In camspeak, it's called creating more area under the curve, as shown when the valve lift is plotted on a graph. "The more quickly the valve opens and dwells in that position," says Godbold, "the greater the space from opening to closing, or beneath the curve, which makes for better performance at all rpm."
Even so, as the numbers climb, so do the cam maker's engine recommendations concerning compression ratio, converter stall, and intended usage. Comp's Xtreme Energy line, for instance, starts out at 200/206 degrees duration at 0.050 (intake/exhaust) and 0.472/0.480 inch lift, a combo that's "good for mileage and for towing" and has a "smooth idle." Just four cams away, its cousin that runs 224/230 degrees duration at 0.050 and 0.502/0.510 lift is for "high-performance street machines" and calls for a 2,000-plus stall converter plus deeper rear gears and warns of a choppy idle. It doesn't take all that much to significantly alter an engine's characteristics, so again, keep your combination and goals in mind when making a pick.
Lobe Separation Angle (LSA)
What it is: The distance between the intake centerline and the exhaust centerline. The angle can be determined by adding the intake and exhaust centerline numbers together and dividing by two (since the cam spins at half the crankshaft's speed). For example, a cam with a 106-degree intake centerline and a 114-degree exhaust centerline has a lobe separation angle of 110 degrees (106 + 114 = 220 2 = 110).
Why it's important: LSA influences engine operation in multiple ways (we've included a chart elsewhere) but primarily determines where peak torque will occur and how broad the torque band will be.
What it is: The amount of time, measured in crankshaft degrees, that both the intake valve and the exhaust valve are open. This situation happens at the end of the exhaust stroke and the beginning of the intake stroke. Increasing lift or duration or decreasing lobe separation angle increases overlap.
Why it's important: Some overlap is desirable, since the outgoing exhaust gases help pull in the fresh intake charge. Too much, however, leads to a contaminated charge that doesn't burn well. An increase in overlap generally improves top-end power at the expense of low-end grunt and reduces idle quality.
What it is: A cam with identical intake and exhaust lobe profiles, employing equal amounts of duration and lift. For example, a Crane Energizer 266 H10 (PN 10004) has 266 degrees advertised duration, 210 degrees duration at 0.050 inch, and 0.440 inch lift on both the intake and exhaust sides.
Why it's important: Some engines, especially those with heads that flow well on the exhaust side, may work best with a single-pattern cam.
What it is: Lobe lift multiplied by the rocker arm ratio. For example, if we have a lobe that measures 0.334 inch and are running a 1.5:1 rocker arm ratio, 0.334 x 1.5 = 0.501 inch valve lift. Running a 1.6:1 rocker arm creates 0.534 inch valve lift.
Why it's important: It's the distance the valve is lifted off its seat at the cam lobe's highest point and influences how much power an engine will make within its rpm range.
What it is: The point of highest lift on the intake lobe, expressed in degrees after top dead center (ATDC). The exhaust centerline is that lobe's highest point of lift, expressed in degrees before top dead center (BTDC).
Why it's important: The intake centerline is used to tie the valve timing to the crankshaft's rotation. The centerline can be altered by installing the cam in an advanced or retarded position.
What it is: A cam with different intake and exhaust profiles. Usually, the exhaust lobe will employ more lift and duration to help evacuate exhaust gas from the cylinders. For example, a Comp XR294HR Xtreme Energy cam (PN 12-443-8) has 294/300 degrees advertised duration (intake/exhaust), 0.224/0.248 duration at 0.050, and 0.540/0.562 inch lift.
Why it's important: Many engine combinations will benefit from the extra lift and duration when it comes to evacuating exhaust gases.
What it is: The amount of time, expressed in degrees of crankshaft rotation, that the valve stays open. Cam makers usually refer to two types of duration:
* Advertised duration is the number of crankshaft degrees that the cam follower is lifted more than a predetermined amount off of its seat. The SAE standard (which not all manufacturers use) is 0.006 inch.
* Duration at 0.050 inch measures the movement of the cam follower, in crankshaft degrees, from the point where it is first lifted 0.050 inch off the base circle on the opening side of the lobe to the point where it descends to 0.050 inch off the base circle on the closing side. Why it's important: Duration determines an engine's rpm range. Larger-duration cams operate at higher rpm at the expense of low rpm power; smaller-duration cams make good low-rpm power but won't rev as high.
What it is: The cam lifter, also known as a follower or a tappet, makes direct contact with the cam lobes and follows the contour, or profile, of the cam.
Why it's important: There are four types of cams and a specific type of lifter for each one: hydraulic flat-tappet, solid flat-tappet, mechanical roller tappet, and hydraulic roller tappet. Flat-tappet lifters should never be reused when installing a new cam.
What it is: The height of each of a Chevy camshaft's 16 lobes above its base circle, measured in thousandths of an inch.
Why it's important: This figure is the amount the lobe actually raises the lifter. It can't be changed, since it's ground into the cam.
If the most frequent mistake cam swappers make is choosing the wrong cam, the second is most certainly neglecting to upgrade the rest of the valvetrain to go with the new 'stick. "Many people may not fully appreciate how each part has to work together," says Knight. "And creating a good, stiff valvetrain is critical." Special attention should be paid to the valvesprings--just because what's already in your cylinder heads can handle an increase in lift doesn't mean they've got the necessary spring rate or pressure for the new cam profile. There's a host of things to check when stepping up your cam--run through this list and you'll have your bases pretty well covered.
|LIFTERS || *Make sure you use the correct lifters for your application. "You can't run hydraulic lifters on a mechanical cam, either flat-tappet or roller," warns Knight. "The incompatible lobe designs can possibly lead to the lifters literally exploding." |
*Never reuse flat-tappet lifters--either solid or hydraulic--on a new cam. These mate to the cam lobe during initial break-in and won't wear in properly on a new cam.
*Be sure to use a break-in oil and either oil additive or diesel oil when first running a hydraulic or solid flat-tappet cam. It may also be a good idea to remove the inner valvesprings for break-in if you're running high spring pressures.
*Roller lifters--either solid or hydraulic--can be reused if they're in good shape.
|PUSHRODS ||*Many guys try to save a buck when it comes to buying pushrods, but investing in good, stiff pushrods can pay dividends. "We took a `nothing' motor, put in good pushrods, and all the little sags and dips came out of the powerband," says Knight. "We've seen increases of 7-9 hp with a pushrod upgrade." |
*Hold off on buying pushrods when you buy your cam and lifters. Instead, use a pushrod length checker to determine the proper pushrod length, then order them. In short, the proper pushrod length is the one that yields correct valvetrain geometry.
*Check pushrod-to-head clearance whenever changing a cam or other valvetrain components.
|ROCKER ARMS || *Traditional stamped-steel rocker arms are fine for stock applications, but any performance application should be using a good set of roller rockers--they're more rigid and cut down on power robbing friction. |
*Increasing rocker arm ratio by a point (e.g., 1.5:1 to 1.6:1) increases valve lift by approximately 0.030 inch and adds 2-4 degrees of duration--most cams specs base valve lift on a 1.5:1 rocker.
*Self-aligning rockers shouldn't be used with guideplates.
|SPRINGS AND HARDWARE ||*Always use springs that are appropriate for your type of cam and are made to handle your intended lift figures and rpm levels. Don't assume the springs you already have will work. Cam manufacturers spell out the spring needed for each application for good reason. "You should never cheap out on valvespings," says Knight. |
*Check for valvespring coil bind--there should always be at least 0.060 inch between both the inner and outer coils. *Likewise, be sure to use the correct retainers and locks with your springs. Check just about any cam catalog, and the proper hardware will be specified.
*Check for rocker arm-to-retainer clearance--you should have at least 0.030 inch.
*Once you have the proper valvespring, be sure to set it up properly--the installed height and seat load are listed on the end of the box. *Remember to check for retainer-to-valveguide--or seal--clearance. The distance between the two should be greater than the valve lift you're running.
*Use of a spring locator, or cup, is mandatory on aluminum heads, and not a bad idea in any case.
|VALVES ||*Be sure to check piston-to-valve clearance whenever you change a cam or any other valvetrain components. You need a minimum of 0.100 inch on the intake and 0.125 on the exhaust. |
Top 5 Camshaft Mistakes from Nolan Jamora, Isky Racing Cams
Overcamming an engine: Most guys just don't have the experience to choose best cam and almost always overcam the engine. Then they call and say they have no bottom end or can't get it to idle and that it's the cam's fault. They should have called first.
Wrong Combination: This happens a lot. A guy buys the same heads his buddy has and the manifold he read about in an article and is running the carb his engine came with and has no idea what his stock converter stalls at yet he puts it all together and thinks it will run great. Now you have a guy with a 600-cfm carb, a single-plane manifold, heads designed for 8,500 rpm, a cam that runs 3,000-7,000 rpm, and a 1,800-stall converter. That's just bad news and a waste of time and money. You have to have all your parts working together and all able to work in the same rpm range as the cam.
Wrong LSA: When you get a good combo going and you order the cam, you have to be aware of the right LSA for your cam. Even if you've picked the right cam for your combo and rpm range, the wrong LSA could still cause problems. If you have two cams with the same lift and duration but one has a 106 LSA and the other a 112, the one with a 106 will have better bottom end and midrange and rough idle but less top end, and the other will have better top end and a smoother idle.
Buying a Cam for Your Next Engine Now: I have guys call all the time for a cam recommendation and tell me what their combo is. Then just after the guy places the order he will say, "So for now I'm gonna put this roller cam in with my Performer manifold and stock heads for a while 'til I can afford the better heads, manifold, and carb. That'll be cool, right? Be smart and buy a cam that works with what you have now, not what you want to have down the road.
Wrong Type of Cam: The choice between hydraulic, solid flat-tappet, hydraulic roller, and solid roller is very important. If your engine comes hydraulic and you only want a little increase in performance, stay hydraulic. If you want to pick up a few thousand rpm and not have to check lash, run a hydraulic roller. If you want the sound and rough idle for a street/strip combo and don't mind adjusting the lash, run a solid flat-tappet. If you are racing, it's almost always best to go full solid roller. Get with a cam tech and go over the setup to pick the right type of cam with the right specs.
When GM created the LS engine family, it increased the cam core size from the traditional 1.868 inches (approximately 47.5 mm) to 2.165 inches, or 55 mm. Lunati has taken this technology a step further by creating an even bigger 60mm core. Why is bigger better? According to James Humphrey, the super-sized cam core was created for use in the LSX block and the World Products Warhawk block. "The LSX can run a 4.250x4.500-inch bore and stroke for 500-plus cubic inches, and it's capable of 2,500 hp," he explains. "The bigger base circle gives better valvetrain dynamics and higher rpm," he continues. "We can be more aggressive with our profiles and maintain stability, since there is little deflection." And while Humphrey admits that we'll "eventually" see street-oriented cores produced, this is definitely a race piece for now.
Crane Cams has been utilizing quick-lift lobe design for as long as the technology has been available--this example is a Powermax Z-Cam hydraulic roller 'stick for a big-block. Crane's roller rocker arms, the Energizer and especially the Gold rockers, have been enthusiast favorites for years and were used in the last of the traditional small-blocks, the 330-horse LT4. The valvespring on the left has been treated with Crane's Mikronite process. It's not a plating or a coating, but rather a surface treatment that reduces friction between mating surfaces, increases metal toughness, and removes minute stress risers created during manufacturing.
CHP: How heavily is Comp involved in racing?
Billy Godbold: Right now, it's close to half of what we do and it's extraordinarily diverse.
CHP: Does what you learn on the track find its way to the street?
BG: There's tremendous trickle-down. It's wild. We've only got one team, and each person has a specialty. Race, OE, street...it's all the same team working on it.
CHP: Can you give us a specific example?
BG: The valve timing events of our Thumpr camshafts are almost identical to road-racing apps, especially 24-hour endurance racing.
CHP: Really? I thought the Thumpr was particularly designed for a "rumpity" sound.
BG: The reason we use that strategy is that drivers get tired and don't want to shift, so this cam lets the car pull if it's a gear high in a turn or a gear low on a straight. You get an early torque peak and a long, gentle fall-off. It's more fun to drive.
CHP: Tell us a bit about designing camshafts.
BG: Mine is the first generation that did cams with a Spintron. Before, we did it by the seat of our pants, on the dyno, and tried to imagine what's going on. With a Spintron, we can see where issues are. It lets us know exactly where we're getting in trouble.
CHP: Any parting words of wisdom?
BG: There's nothing wrong with not being able to afford everything at once. You just need to have a plan, the what, where, and how, to create an awesome street combo.
Comp Cams has been hard at work on its Thumpr line of retrofit hydraulic roller and hydraulic flat-tappet camshafts, which are designed to sound off with a lopey idle but maintain a wide, torquey powerband. The cams now come in three versions: Thumpr, Mutha Thumpr, and Big Mother Thumpr, as pictured here. Comp has also introduced a new line of CNC-machined aluminum roller rockers, Ultra-Gold aluminum, which will clear up to a 1.650-inch-od valvespring. We also checked out a couple of Comp's trick new Lightweight Tool Steel retainers, which are only 2-4 grams heavier than titanium but cost half as much.
Lunati rounded out its popular Voodoo line of cams with a new solid flat-tappet version, and has been hard at work creating improved springs and other valvetrain components to work with these popular 'sticks. Three new solid lifters were created to go with the new cams--all are micropolished, which Humphrey says reduces the friction at this vital contact point. And of course, you can't miss Lunati's new Voodoo roller rocker arms, which the company says have a larger bearing and trunnion for improved durability, load capacity, and stability. The roller-tip shaft is secured with an internal C-clip to guard against failure.
Isky was already making solid roller LS cams, and now has multiple new hydraulic roller 'sticks to go with them. These guys have been hard at work on this side of the street, creating new lifters, pushrods, and traditional and B-Hive valvesprings, as well as machined steel locks retainers, and locators.
Q&A:James Humphrey, Lunati
CHP: What was the genesis of the Voodoo line?
James Humphrey: Lunati has made excellent cams, but in today's marketplace, if you stay with the same thing, you don't last.
CHP: So what's different about the Voodoo cams?
JH: The lobe acceleration rate, the increased area under the curve, and our unique approach to duration at 0.050. We've also paid attention to lobe separation. Wider separation makes for a wider powerband. The Voodoo cams have a 110- and 112-degree LSA, which means they'll work with aftermarket four-barrels and OEM computers.
CHP: What did you mean about your approach to duration at 0.050 inch lift?
JH: With the advent of improved heads and valvesprings, we can get away with a lot more than we used to. That means bigger, better profiles. You get more air throughout the range with a quality head.
CHP: Have you introduced any other new pieces?
JH: We've added beehive springs and a line of pacalloy springs, which are extremely high quality yet affordable. We've also added retainers and locks as well as new solid lifters.
CHP: What trends are you seeing in what the public wants?
JH: I still see a lot of hydraulic flat-tappet action, but the trend is leaning more and more toward hydraulic rollers. You don't have to rely on maintenance or rotation but can still get fairly aggressive.
Crower has camshafts for just about any application, though we think it's fair to say much of its clientele leans toward the hot street and racing side of the game. The cam shown is a solid roller 280R piece intended for the former, along with some of Crower's Severe-Duty cutaway lifters and titanium retainers. The company makes aluminum stud-mount rockers, of course, and its shaft-mount systems are available in aluminum or stainless steel, in a variety of offsets.
"One of the absolute killers to high-end horsepower is lack of valvetrain stiffness, Comp's Billy Godbold tells us. "You lose stability, and even if you can control the valve with its spring, things start to bend." As a result, duration--and therefore high-rpm horsepower--is lost. When should you look into using a stud girdle? Godbold actually surprised us with his answer. "If you're going racing with stud-mounted rocker arms, you should use one, but if you have the right cam, you should be running fairly close to its limit speed; you should be on its dynamic threshold." In other words, when you've already upgraded everything else in your valvetrain and are running near its limit, it's time to consider a stud girdle. "If you're after that last 5-10 hp, you should look into it," says Godbold. "It lets you lock all the studs together, and if you have a stiffer upper valvetrain you have more duration."
Pushrods can get overlooked when putting together a valvetrain, but using good, stiff rods is critical to maintaining valvetrain stability. Stock pushrods don't cut it in any performance application; Crane's three-piece pushrods are a significant step up, and its one-piece, heat-treated chrome-moly pieces are better still. It's also important to always measure for pushrod length using an adjustable tool like the one shown.
For the ultimate in upper valvetrain stiffness, of course, only a shaft-mount rocker arm system will do, and these setups are a Jesel specialty. The rocker arms are locked into a single bar running across the head, keeping rocker arm flex--and the resulting losses in duration, lift, and therefore performance--at an absolute minimum. If you're working the track and turning high rpm, shaft mounts should be considered. Jesel's setups start at about $800.
Timing chains stretch over time, so it's always a good idea to install a new chain and sprocket set like these Crane pieces when swapping in a new cam. The traditional small-block set on the left is a three-position piece, which allows the cam to be installed straight-up, 4 degrees retarded, or 4 degrees advanced. The billet sprocket LS1/LS6 timing set on the right allows for 5 degrees of adjustment either way by simply loosening the six Allen-head bolts and rotating the cam sprocket.
Speaking of advancing or retarding... As we've noted earlier, a cam's intake/exhaust centerline is the theoretical maximum lift point on the lobe, expressed in degrees after TDC. This centerline is used to tie the valve timing to the crankshaft rotation. Almost all our cam experts agree that cams tend to run best with a bit of advance in place, so the 'sticks come ground to deliver this advance when installed in the straight-up position. A multiple-position timing set allows you to move the intake centerline forward or back. What happens if you advance or retard the cam? With the former, the rpm range is moved down; with the latter, it's shifted upward. Knight recommends always starting out at the straight-up position. "You can refine from there," he says, "but if you're seeing a benefit from moving more than 8 degrees advanced or any degrees of retard from 0, you don't have the right cam."
Proper-length pushrods are also the key to creating correct valvetrain geometry. In short, with the right pushrod in place, the rocker-arm tip rolls from the intake side of the valve tip, across its center as the cam reaches midlift, to the exhaust side of the tip at full lift, then back to the intake side. It's a relatively simple measurement to take and implement, but it pays off in valvetrain longevity and improved perrformance.
Cam cards come in a variety of configurations, but they all serve the same purpose, which is to tell you just about everything you should know when it comes to your cam: its lobe separation angle, intake centerline, each of the valve opening and closing events, valve lift, advertised duration, and duration at 0.050 inch. This Comp card refers to a hydraulic flat-tappet cam, so the valve adjustment spec shows zero; with a solid or solid roller cam, the lash setting would be shown. This card also reminds the installer that new valvesprings will be needed for this 'stick to work properly; a quick call to Comp with some cylinder heads specifics will yield a recommendation. CHP
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