Camshaft basics and Understanding

Okay guys I have put together some camshaft information I think that will help all of us to understand the camshaft and its operation better. This will help us to really know what we need to look for when chosing a cam


Camshaft Attributes
1. Intake lobe lift, 2. Exhaust lobe lift, 3. Intake duration, 4. Exhaust duration, 5. Overlap, 6. Lobe Centerline Angle (LCA), 7. Cam Advance (A) and Retard (R). View Related Article

 

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Intake Duration
Here's the intake cycle from start to finish. The duration (in this example 270 degrees) is indicated by arrow 3. The degrees opening before TDC is indicated by arrow 1, and the degrees after BDC to the closing point by arrow 2. Number 4 indicates the intake centerline angle, which is exactly halfway between the opening and closing point.

 

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Example Cam Card
Check out the intake duration alongside the exhaust duration, depicted in the same manner as the intake. Remember, the engine turns two revolutions (720 degrees) for a complete cycle of events to take place. By melding the intake and exhaust duration arcs together, we form the valve opening event diagram at the bottom. In this example, the intake opens (IO) 25 degrees before TDC and closes 55 after. The exhaust opens (EO) 55 degrees before BDC and closes 25 after TDC. The way we would quote the events of this cam are 25-55-55-25. The overlap, that's when both the intake and exhaust are open, is indicated here, and in this case is 50 degrees

 

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Lobe Lift and Duration
Duration number one is the duration at a solid lifter's lash point. The lash point at the lifter is the lash at the rocker, divided by the rocker ratio. Arrow two is the so-called "advertised duration" and is usually 0.006 inch (6 thousandths) for hydraulics and 0.020 inch (20 thousandths) for solids. The red arrow indicates the duration at 0.050 inch (50 thousandths).

 

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Overlap Kills Vacuum--Here's Why
Depicted here are two consecutively inducing cylinders of a V-8. The right-hand cylinder is halfway through the induction stroke and is moving down the bore at near its maximum speed. The left-hand cylinder is in the overlap period. Because a single-plane intake allows all cylinders to communicate, it is easier for the right-hand cylinder to draw in exhaust from the exhaust port of the left cylinder through the open valves. The smaller of the red circles is about equal to the overlap through the flow area of a 280-degree cam on a 108 LCA while the larger one is equal to a 300 race profile on a 108 LCA. The blue circle represents the through-flow area of a four-barrel cab at idle. The overlap area looks like a large hole in the intake, as far as generating vacuum is concerned.

 

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Rocker Geometry
A rocker's ratio is usually defined as R1 divided by R2 but, because of the geometric relationship between points A, B and C, the ratio changes as the rocker progresses through its lift range. If pickup point "C" is moved in the direction of the ghosted arrow, the ratio of the rocker, as it lifts the valve off its seat, will be higher. So long as no dynamic problems are encountered, this is good for added output, especially with short-cammed engines.