![]() The amount of lift that can be used by a particular head depends on how much flow the cylinder head ports can deliver and at what valve lift the port flow stops increasing. Read more: The Basics Of Lift, Duration, And A Whole Lot More by Jeff Smith (February, 2009 Chevy High Performance). The lobe lift is ground into the cam, however the actual lift seen at the valve can be changed by using a different rocker arm ratio. Lobe lift is measured by subtracting the base circle diameter from the maximum height of the eccentric (including the base circle). Lobe lift is how far the lobe of the cam will move the lifter in a linear fashion. The valve lift is found by multiplying the lobe lift by the rocker arm ratio. When you look at the cam specifications card (typically referred to simply as a cam card), it will list several numbers that will dictate how this particular cam will operate in your engine. The article and video will make many of the ideas and terms used in this article much clearer.įor some more advanced information on camshaft operation and definition the specs of a camshaft, see Secrets of Camshaft Power by Marlan Davis (Car Craft, December, 1998). If further explanation or a refresher is needed, see Camshaft 101: How do cams work?. This article assumes that the basics of how and what a camshaft does is understood. The shape of the cam lobe dictate when the valve opens and closes in relation to crankshaft position (aka the cam timing), and how far the valve is opened (aka the valve lift), as well as how long the valve is open and closed (aka the duration). The rocker arm directs the motion of the cam lobe to the valve, lifting the valve open and closing it shut with the aid of the valve spring(s). The lifter is linked to a fulcrum, or rocker arm by a pushrod. As the cam turns, the eccentric-shaped cam lobe lifts and lowers a cam follower, or lifter. Mechanically speaking, the camshaft is linked to the crankshaft and turns 1/2 the speed of the crank. The main focus of this article will be on a conventional OHV (overhead valve), cam-in-block engine configuration using two valves per cylinder, as shown above. The camshaft can be thought of as the brain of the engine, and it has a very large effect on the amount of power an engine makes as well as where in the rpm range that power occurs. ![]()
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