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. |