Cam and compression ratio compatibility
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===Advanced Reading and Engine Theory=== | ===Advanced Reading and Engine Theory=== | ||
| − | Intake valves close after the piston travels ''' | + | Intake valves close after the piston travels '''past''' bottom dead center (ABDC). This sounds counter-intuitive, but this design aspect was a break through in modern engines and has allowed them to make more power as well as run at higher RPM's. The reason why is all about the Dynamic Compression Ratio (DCR). Air is a gas and as such is compressible (unlike liquids or solids). When air enters the engine is does so at a high velocity, and when the piston reaches bottom dead center, due to momentum, the air wants keeps moving in and starts to compress. In short, the longer the intake valve stays open, the more air can be packed into the cylinder. |
The extent to which intake valves stay open is measured in degrees. IVC (Intake Valve Closing), is one of, if not the most important determining factor in how the cam shaft impacts engine performance. Manufacturers will give this value in degrees ABDC (after bottom dead center). As an example, the Comp Cams XE275H cam's intake valve closes 64º ABDC. | The extent to which intake valves stay open is measured in degrees. IVC (Intake Valve Closing), is one of, if not the most important determining factor in how the cam shaft impacts engine performance. Manufacturers will give this value in degrees ABDC (after bottom dead center). As an example, the Comp Cams XE275H cam's intake valve closes 64º ABDC. | ||
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