Page 4 of Lunati Camshafts by Holley Performance Products, Inc.

cams lift lift refers to maximum valve lift this is how much the valve is lifted off its seat at the cam lobe s highest point valve train how is it measured valve lift is the amount usually in inches that the valve is lifted off of its seat it is usually measured with a dial indicator at the tip of the valve lobe lift is the amount usually in inches that the cam lobe increases in radius above the cam base circle tip to quickly find maximum lobe lift measure the base circle of the cam and subtract it from the thickness across the cam lobe s highest point see the diagram below tip maximum valve lift can be calculated by multiplying the maximum lobe lift times the rocker ratio for example a 0.310 lobe lift cam yields 0.496 of valve lift when using a 1.6 ratio rocker arm formula valve lift lobe lift x rocker ratio base circle and lobe lift pistons base circle lobe lift base circle and lobe lift base circle rods what does it do the intake and exhaust valves need to open to let air/fuel in and exhaust out of the cylinders generally opening the valves quicker and further will increase engine output increasing valve lift without increasing duration can yield more power without much change to the nature of the power curve however an increase in valve lift almost always is accompanied by an increase in duration this is because ramps are limited in their shape which is directly related to the type of lifters being used such as flat or roller cranks duration duration is the angle in crankshaft degrees that the valve stays off its seat during the lifting cycle of the cam lobe how is it measured advertised duration is the angle in crankshaft degrees that the cam follower is lifted more than a predetermined amount the sae standard is 0.006 off of its seat duration 050 is a measurement of the movement the cam follower in crankshaft degrees from the point where it s first lifted .050 off the base circle on the opening ramp side of the camshaft lobe to the point where it ends up being .050 from the base circle on the closing ramp side of the camshaft lobe this is the industry standard and is a good value to use to compare cams from different manufacturers both are usually measured with a dial indicator and a degree wheel engine kits what does it do increasing duration keeps the valve open longer and can increase high-rpm power doing so increases the rpm range that the engine produces power increasing duration without a change in lobe separation angle will result in increased valve overlap apparel tech line 662-892-1500 5

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