How to choose a camshaft
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====Narrower LSA:==== | ====Narrower LSA:==== | ||
| − | A narrower LSA will ''increase'' overlap. This has a tendency to | + | A narrower LSA will ''increase'' overlap. This has a tendency to increase engine output at lower RPM and decrease engine output at higher RPM. A narrower LSA tend to make less peak power but more average power. |
*Moves torque to lower RPM | *Moves torque to lower RPM | ||
*Increases maximum torque | *Increases maximum torque | ||
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===Overlap=== | ===Overlap=== | ||
[[File:Overlap estimator1.jpg|thumb|right|300px|Area '''1''' is for street towing, '''2''' is regular street, '''3''' is street performance, '''4''' is street/strip, '''5''' is race, and '''6''' is Pro race.]] | [[File:Overlap estimator1.jpg|thumb|right|300px|Area '''1''' is for street towing, '''2''' is regular street, '''3''' is street performance, '''4''' is street/strip, '''5''' is race, and '''6''' is Pro race.]] | ||
| − | "Overlap" represents the amount of duration in camshaft degrees when both the exhaust and intake valves are open at the same time. | + | "Overlap" represents the amount of duration in camshaft degrees when both the exhaust and intake valves are open at the same time. For a single cam engine this factor is ground into the cam and can't be changed without physically altering the camshaft lobe profiles. On a dual overhead camshaft (DOHC) engine overlap can be altered with adjustable cam gears. Adjusting one or more cams closer to TDC increases overlap. Increasing duration at the same LSA will increase overlap. Decreasing LSA at the same duration will also increase overlap. |
| − | Overlap is usually not found printed out on the cam card, but it's easy to calculate. *Add the intake opening point BTDC to the exhaust closing point ATDC. | + | Overlap is usually not found printed out on the cam card, but it's easy to calculate. |
| + | *Add the intake opening point BTDC to the exhaust closing point ATDC. | ||
If the intake opening and exhaust closing points aren't known, you can estimate the overlap by using the '''advertised duration''' (or duration @ 0.050" lift, etc.) and the '''lobe separation angle'''. | If the intake opening and exhaust closing points aren't known, you can estimate the overlap by using the '''advertised duration''' (or duration @ 0.050" lift, etc.) and the '''lobe separation angle'''. | ||
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===Lobe intensity=== | ===Lobe intensity=== | ||
| − | One more point about the cam profile is lobe intensity. For a given duration, more lift means the lobe ramps (the opening and closing faces on the sides of the lobe) are steeper (more intensity). That is to say, the cam lobe | + | One more point about the cam profile is lobe intensity. For a given duration, more lift means the lobe ramps (the opening and closing faces on the sides of the lobe) are steeper (more intensity). That is to say, the cam lobe has to accelerate the lifter faster to get to the peak lift within the available amount of duration duration. Faster ramp speed can give more "area under the curve", which usually equates to a broader, less peaky powerband. The downside for flat tappet cams is that the steeper ramps mean they contact the lifter at a greater angle, so the potential for wiping out a cam lobe or lifter is greater. Manufacturers are well aware of this, so they try to design the lobe profiles to optimize power, yet maintain good durability. Cam profiles like the Comp Cams XE-series and Lunati's Voodoo line are both at the edge of how fast the valve can be safely opened and closed. That's why they caution against using a higher ratio rocker arm when using these grinds. More on lobe intensity can be seen [http://www.harveycrane.com/duration.htm '''at this page'''] by Harvey Crane of Crane Cams. |
===Intake centerline (ICL)=== | ===Intake centerline (ICL)=== | ||
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==Solid vs. hydraulic camshaft== | ==Solid vs. hydraulic camshaft== | ||
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==Flat tappet vs. roller== | ==Flat tappet vs. roller== | ||
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==Custom cams== | ==Custom cams== | ||
Choosing a cam is often something that seems shrouded in mystery. The manufacturers have a hundred years of technology to draw from and millions of dollars and man-hours expended on the research, development and testing of camshafts. They have used that experience to come up with thousands of lobe profiles and grinds that attempt to cover the whole broad spectrum of engines and applications. It's possible that an off-the-shelf grind might be perfectly fine, but it can't hurt for you to look into a custom designed/ground camshaft if a particular combination falls between what's readily available. Most all the cam companies will set you up with a custom ground cam for a fee. And most companies have tech lines and web sites to help you pick the right grind. Take the manufacturer's expertise and recommendations into account when deciding on a cam. | Choosing a cam is often something that seems shrouded in mystery. The manufacturers have a hundred years of technology to draw from and millions of dollars and man-hours expended on the research, development and testing of camshafts. They have used that experience to come up with thousands of lobe profiles and grinds that attempt to cover the whole broad spectrum of engines and applications. It's possible that an off-the-shelf grind might be perfectly fine, but it can't hurt for you to look into a custom designed/ground camshaft if a particular combination falls between what's readily available. Most all the cam companies will set you up with a custom ground cam for a fee. And most companies have tech lines and web sites to help you pick the right grind. Take the manufacturer's expertise and recommendations into account when deciding on a cam. | ||
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| + | ===Another View=== | ||
| + | This is no longer true. There happens to be a mathematical equation that you can use to calculate exact values for valve seat durations, net valve lift, rate of lift and lobe centerlines. It has been around for years, and was written by Dick Jones, used by Mike Jones at Jones Cams, and written into an easy to use and inexpensive camshaft requirement software. It gives you the exact values for valve seat duration, durations @ .014, .016, .018, .020, .050, .100, .200, .300, .400, net valve lift, cam lobe lift, lift @ TDC, lobe centerlines and profile footprint. It takes 3 to 4 minutes and has been proven to be accurate over the past 30 years. There is nothing as accurate. Controlled Induction camshaft requirement software guarantees it. | ||
==Simulation software== | ==Simulation software== | ||
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