Cam and compression ratio compatibility
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On the other hand, it's equally as foolish to install a short cam into a motor with a fairly high static compression ratio. You get into an area of such high cylinder pressure that no fuel short of alcohol or racing gasoline will prevent detonation. | On the other hand, it's equally as foolish to install a short cam into a motor with a fairly high static compression ratio. You get into an area of such high cylinder pressure that no fuel short of alcohol or racing gasoline will prevent detonation. | ||
| − | You can move 1/2 point of SCR either way and be in the ballpark. In other words, if you have a 9.00:1 motor and you want a little more cam, you can move up to a cam that would be used in a 9.5:1 motor and be | + | You can move 1/2 point of SCR either way and be in the ballpark. In other words, if you have a 9.00:1 motor and you want a little more cam, you can move up to a cam that would be used in a 9.5:1 motor and be OK. On the other hand, if you wanted to go with a little less cam, you might use 1/2 point less compression, down to an 8.50:1 cam. |
| − | + | [http://www.cranecams.com/faqview.php?s_id=9 Crane] says: | |
| − | http://www.cranecams.com/faqview.php?s_id=9 | + | <blockquote> |
| + | '''Why is it necessary to know the Compression Ratio of an engine in order to choose the correct cam?'''</blockquote> | ||
| + | <blockquote>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 (at .050" lifter rise) and the position of the cam in the engine (advanced or retarded). 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.)</blockquote> | ||
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| + | <blockquote>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.</blockquote> | ||
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| + | <blockquote>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.</blockquote> | ||
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