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What is meant by Basic RPM?
The camshaft's basic RPM is the RPM range within which the engine will produce its best power. The width of this power band is approximately 3500 to 4000 RPM with roller lifter cams. It is important that you select the camshaft with the "Basic RPM Range" best suited to your application, vehicle gearing and tire diameter.

Why is Cruise RPM at 60 MPH important?
When selecting a new camshaft, you can raise or lower the engine's basic RPM range. It is important to be sure the drive train is capable of matching your selection. The cruise RPM at 60 MPH is a way of rating your rear end gearing and tire diameter to determine if these components match the RPM potential you are desiring.


What is Camshaft Duration and why is it important?
Duration is the period of time, measured in degrees of crankshaft rotation, that a valve is open. Duration (at .050" lifter rise) is the deciding factor to what the engine's basic RPM range will be. Lower duration cams produce the power in the lower RPM range. Larger duration cams operate at higher RPM, but you will lose bottom end power to gain top end power as the duration is increased. (For each ten degree change in the duration at .050", the power band moves up or down in RPM range by approximately 500 RPM.)


What is the difference in Advertised Duration and Duration at .050" Lifter Rise (Tappet Lift)?
In order for duration to have any merit as a measurement for comparing camshaft size, the method for determining the duration must be the same. There are two key components for measuring duration-- the degrees of crankshaft rotation and at what point of lifter rise the measurements were taken. Advertised durations are not taken at any consistent point of lifter rise, so these numbers can vary greatly. For this reason, advertised duration figures are not good for comparing cams. Duration values expressed at .050" lifter rise state the exact point the measurement was taken. These are the only duration figures that are consistent and can accurately be used to compare camshafts.


How does Valve Lift affect the operation of an engine?
Lift is the distance the valve actually travels. It is created by the cam lobe lift, which is then increased by the rocker arm ratio. The amount of lift you have and the speed at which the valve moves is a key factor in determining the torque the engine will produce.


What is Camshaft Lobe Separation and how does it affect the engine?
Lobe separation is the distance (in camshaft degrees) that the intake and exhaust lobe centerlines (for a given cylinder) are spread apart. Lobe separation is a physical characteristic of the camshaft and cannot be changed without regrinding the lobes.

This separation determines where peak torque will occur within the engine's power range. Tight lobe separations cause the peak torque to build early in basic RPM range of the cam. The torque will be concentrated, build quickly and peak out. Broader lobe separations allow the torque to be spread over a broader portion of the basic RPM range and shows better power through the upper RPM.


What are Intake and Exhaust Centerlines?
The centerline of either the intake or exhaust lobe is the theoretical maximum lift point of the lobe in relationship to Top Dead Center in degrees of crankshaft rotation.


How does Advancing or Retarding the camshaft's position in the engine affect performance?
Advancing the cam will shift the basic RPM range downward. Four degrees of advance (from the original position) will cause the power range to start approximately 200 RPM sooner. Retarding it this same amount will move the power upward approximately 200 RPM. If the correct cam has been selected for a particular application, installing it in the normal "straight up" position is the best starting point.


Why is it necessary to know the Compression Ratio of an engine in order to choose the correct cam?
The compression ratio of the engine is one of three key factors in determining the engine's cylinder pressure. The other two are the duration of the camshaft and the position of the cam in the engine. The result of how these three factors interact with one another is the amount of cylinder pressure the engine will generate. (This is usually expressed as the "cranking pressure" that can be measured with a gauge installed in the spark plug hole.)

It is important to be sure that the engine's compression ratio matches the recommended ratio for the cam you are selecting. Too little compression ratio (or too much duration) will cause the cylinder pressure to drop. This will lower the power output of the engine.

With too much compression ratio (or too little duration) the cylinder pressure will be too high, causing pre-ignition and detonation. This condition could severely damage engine components.


How does Cylinder Pressure relate to the octane rating of today's unleaded fuel?
In very basic terms, the more cylinder pressure we make the more power the engine will produce. But look out for the fuel! Today's pump gas is too volatile and cannot easily tolerate high compression ratio and high cylinder pressure without risking detonation. Fuel octane boosters or expensive racing gasoline will be necessary if too much cylinder pressure is generated.


Must new (Standard Design) lifters always be installed on a new camshaft?
It's not a must but it is a good idea. These parts will be mated to one another during the initial break-in period. Used lifters sometimes will not mate properly. If you are rebuilding an engine and plan to re-use the lifters it can be done, as long as the lifter goes back in the same place and direction.


What is the Most Important thing to remember?
Reading and following the instructions in your factory service manual is most important. If there is something you don't understand, contact us. Get answers to your questions before proceeding. Any camshaft and lifters must be pre-lubricated before installation.


What Types of Mechanical Interference Should You Look Out For?
When you increase the valve lift with a bigger cam you must be sure that there is no interference between any of the moving parts. Some of the components that must be inspected for clearance are: Rocker box and cover, crank bearing boss and other nearby case casting areas, the distance from the bottom of the valve spring retainer and the top of the valve stem guide.