Camshaft Fundamentals
Centerline
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.
Dual-Pattern Cam
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.
Duration
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.
Lifter
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.
Lobe Lift
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.
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.
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 valve springs, as well as machined steel locks, retainers, and locators. | 
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. |