How to choose a camshaft
(→Overlap) |
(→Overlap) |
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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. For a single cam | + | "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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