How to choose a camshaft
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| − | The camshaft is the brain of your engine | + | The camshaft is the brain of your engine, mechanically opening and closing the valves. It dictates when the valves open and close, how long they are open and closed and when they are open and closed in relation to crankshaft position. The camshaft has a very large effect on the type of power your engine makes. |
[[http://www.rehermorrison.com/images/Camshaft_Valvetrain/Camshaft.jpg]] | [[http://www.rehermorrison.com/images/Camshaft_Valvetrain/Camshaft.jpg]] | ||
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[[http://www.marinediesels.info/animations/rocker3.gif]] | [[http://www.marinediesels.info/animations/rocker3.gif]] | ||
| − | This article assumes that you already know the most basic fundamentals of camshaft operation and starts with | + | This article assumes that you already know the most basic fundamentals of camshaft operation and starts with describing camshaft parameters. It is designed to help you select the right cam and decipher the numbers so you know WHY its a good cam. For more basic information on camshaft operation and the definition of its components, I suggest www.howstuffworks.com |
| − | When you look at cam | + | When you look at cam specifications (typically referred to as a cam card), they will list several numbers that are very important to how this particular cam will operate in your motor. The photo above outlines a pushrod engine which is what you'll encounter most of the time in the hotrodding world. The cam is located in the block. The lobes push against lifters which push on pushrods, and the pushrods transfer their motion to the rockers. This in turn operates the valves. |
=== What do all the numbers mean? === | === What do all the numbers mean? === | ||
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'''Duration.''' | '''Duration.''' | ||
| − | This is the amount of time (stated in crankshaft degrees) that the cam will hold the valve off the seat. Some cams have the same duration for the intake and exhaust valves. | + | This is the amount of time (stated in crankshaft degrees) that the cam will hold the valve off the seat. Some cams have the same duration for the intake and exhaust valves. They are typically called single pattern cams. Those with different numbers for intake and exhaust are often called split pattern or dual pattern. The design is ground into the cam and can't be altered without physically changing the camshaft lobe profiles. |
'''Lift.''' | '''Lift.''' | ||
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'''LSA''' | '''LSA''' | ||
| − | Lobe Separation Angle, sometimes called Lobe Center Angle. | + | Lobe Separation Angle, sometimes called Lobe Center Angle or Lobe Displacement Angle. This is a measurement in ''camshaft'' degrees that tells you how far apart the centerlines, or maximum lift points of the exhaust and intake lobes are. This number is ground into the cam and can't be altered without physically changing the camshaft lobe profiles. |
[[http://www.lunaticamshafts.com/Images/Tech/Cams/LobeSeparationSmall.gif]] | [[http://www.lunaticamshafts.com/Images/Tech/Cams/LobeSeparationSmall.gif]] | ||
'''Overlap''' | '''Overlap''' | ||
| − | This number (usually not found on the cam card) represents the amount of duration in camshaft degrees | + | This number (usually not found on the cam card) represents the amount of duration in camshaft degrees when both the exhaust and intake valves are open at the same time. This factor is ground into the cam and can't be changed without physically altering the camshaft lobe profiles. Increasing duration at the same LSA will increase overlap. Decreasing LSA at the same duration will also increase overlap. |
| − | ''' | + | '''Intake and Exhaust Centerlines''' |
| − | Intake | + | Intake Centerline. This number represents where the intake lobe's peak lift occurs in relation to crankshaft rotation. It is the point of maximum lift of the intake lobe and is measured in ''crankshaft'' degrees. A cam ground "straight up" will mean that the exhaust lobe's peak lift will happen at the same amount of degrees before top dead center, as the intake valve will peak after top dead center. ICL is machined into the cam. When cam manufacturers machine the snout of the cam for the cam sprocket, they will drill the holes with the cam slightly advanced, retarded, or straight up. When installed with stock components, the ICL can't be altered. Aftermarket timing chains and sprockets often have provisions for altering how the sprocket attaches to the cam and therefore you can counteract the ICL ground into the cam. If the LSA value is the same as ICL, the cam is ground "straight up." If the ICL is less than the LSA, it is ground advanced by the difference. If ICL is more than the LSA, the cam is ground retarded. For instance, if the cam has a 110-degree LSA with a 106 ICL, the cam is advanced by 4 degrees. |
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| + | Exhaust Centerline. This number represents where the exhaust lobe's peak lift occurs in relation to crankshaft rotation. It is the point of maximum lift of the exhaust lobe and is measure in crankshaft degrees. | ||
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| + | '''Phasing the camshaft''' | ||
| + | While is is true that you cannot change the lobes of a camshaft after it is ground (unless you re-grind the lobes), you can alter the characteristics of the camshaft in your motor by installing it in either a retarded or advanced position relative to the crankshaft rotation. For instance, the manufacturer recommends the camshaft to be installed straight up, neither advanced or retarded from his design. However, you have determined that you are making too much horsepower down low and can't hook the tires up. You want to trade off a little of the lower end power for some higher end power. You might, in this case, install the camshaft slightly retarded. Although all four events (intake open, intake close, exhaust open, exhaust close) will be affected by changing the camshaft timing, the most important one will be the intake closing point. If you retard the camshaft, you will be closing the intake later, thus bleeding off some of the cylinder pressure and resulting in less low end power. Vice versa if you advance the camshaft. More bottom end, less top end. | ||
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(to ba ammended later) | (to ba ammended later) | ||
| + | == Things that will "frag" a camshaft and lifters == | ||
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| + | 1. Failure to remove all rust-preventative from cam and lifters with solvent once you get them home. | ||
| + | 2. Failure to wash the cam and lifters with hot soapy water to remove the remainder of rust-preventative not removed with solvent. | ||
| + | 3. Failure to properly massage an extreme pressure lubricant such as Molybdenum Disulfide into the pores of the metal on all lobes and lifter faces. | ||
| + | 4. Failure to use an extreme pressure lubricant additive to the engine oil for camshaft break-in. | ||
| + | 5. Failure to use the proper valve springs for cam break-in. You can't use the 350 lb over-the-nose springs that you'll eventually use in the motor and expect the cam to live. | ||
| + | 6. Failure to check for valve spring coil bind. | ||
| + | 7. Failure to check for retainer to valve guide clearance. | ||
| + | 8. Failure to check for binding at the rocker/stud interface. | ||
| + | 9. Failure to check for piston/valve clearance. | ||
| + | 10. Failure to run the motor at high rpms for the first 35-40 minutes of its life. NO IDLING. NO IDLING. NO IDLING. | ||
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