Cam and compression ratio compatibility
m (→Advanced Reading and Engine Theory) |
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Performance cams with longer durations, are exactly the opposite. At low RPM's since the intake valve stays open longer ABDC, more of the intake charge is reversed. Hence there is less pressure build up on the compression stroke. To compensate for this, a higher SCR is used. As the RPM's climb, so does the intake charge velocity, thus more air is able to cram itself into the cylinder. Even though the piston is moving up ABDC, the air is compressing upon itself, and able to move into the cylinder because the intake valve is still open. As you can see, at higher RPM's these cams are able to more completely fill the cylinder with air and are able to make more power. These engines have a high SCR and low DCR. They make power at higher RPM's. Since there is a lot of reversion, these engines idle very rough (have a lot of lope). If you were to put a compression tester on these engines you would see something in the 125-150 PSI range. | Performance cams with longer durations, are exactly the opposite. At low RPM's since the intake valve stays open longer ABDC, more of the intake charge is reversed. Hence there is less pressure build up on the compression stroke. To compensate for this, a higher SCR is used. As the RPM's climb, so does the intake charge velocity, thus more air is able to cram itself into the cylinder. Even though the piston is moving up ABDC, the air is compressing upon itself, and able to move into the cylinder because the intake valve is still open. As you can see, at higher RPM's these cams are able to more completely fill the cylinder with air and are able to make more power. These engines have a high SCR and low DCR. They make power at higher RPM's. Since there is a lot of reversion, these engines idle very rough (have a lot of lope). If you were to put a compression tester on these engines you would see something in the 125-150 PSI range. | ||
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| + | You can fine tune a particular cam by advancing or retarding it. This procedure does nothing to alter the lift, duration, lobe seperation, etc of the cam. All you do is change the phase of the cam shaft in relation to the crank. If you advance the cam, then as the name suggests you close the intake valve sooner (this will build more pressure in the cylinder and shift the power band lower). Advancing the cam will cause the intake valve to close later (this will build less pressure in the cylinder and shift the power band higher). | ||
===Dynamic compression ratio calculators=== | ===Dynamic compression ratio calculators=== | ||
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