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.
Tappet Selection
It's usually the first choice made when swapping cams, and there are four options to choose from: hydraulic flattappet, hydraulic roller, solid flat-tappet, and solid roller. We've listed the types in order of increasing power potential, but each has advantages and dis advantages. 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.
Hydraulic Flat-Tappet
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.
Hydraulic Roller
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.
Mechanical Flat-Tappet
Also called a solid tappet, since it provides a solid link between the camlobe 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.
Mechanical Roller
The best of both worlds, this type of lifter allows for the more aggressive lobe designs of a roller setup along with highrpm 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.
Hint: 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.
Duration
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."
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, flattappet 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. |