Editing How to choose a camshaft (section)
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===Lift=== The valve lift is found by multiplying the lobe lift by the rocker arm ratio. Lobe lift is how far the lobe of the cam will move the lifter in a linear fashion. Lobe lift is measured by subtracting the base circle diameter from the maximum height of the eccentric (including the base circle). 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. Read more: [http://www.chevyhiperformance.com/techarticles/148_0307_basic_camshaft_info/index.html '''The Basics Of Lift, Duration, And A Whole Lot More'''] by Jeff Smith (February, 2009 Chevy High Performance). ====Port flow==== 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. More lift is generally better, provided the valves, retainers, pushrods and springs are properly matched to the cam profile and rpm the engine will turn, and if the port flow will support the valve lift without the port "stalling" or going into turbulence that keeps the flow from increasing. If head port flow stalls or starts decreasing above a certain lift, there is no reason to try to use more than that amount lift. But more lift is better, up to the point where the heads start losing flow. Head flow for common domestic head castings can be found [http://users.erols.com/srweiss/tablehdc.htm '''here''']. Heads are flow tested at different valve lifts, and many times the ports are tested at different amounts of "depression" (usually measured in inches of water or "in/H2O"). The results will be expressed as cubic foot per minute (CFM) of air flow. When comparing heads and their ports, be sure the depression is similar (28 in/H2O is a commonly used depression), or be prepared to convert the results from one depression to another depression, using a calculator. Another difference that is often found when comparing flow is the size of the cylinder the head is sitting over (a larger cylinder usually means better flow numbers). Some heads are wet flowed (the air is mixed with a fluid to simulate a working engine) while other heads are dry flowed (just air is used). And yet another difference that may be found is whether an intake manifold is in place during testing (rarely done), or if an exhaust tube is in place (more common), or if clay is used to radius the openings (fairly common). Unfortunately, these differences can make comparing different heads much more difficult.
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