Pump gas compression

I found this in other forum. This guy have same problem to understant this like i have.

"The problem with dynamic compression ratio is that is doesn't take into account the pressure waves of the intake, exhaust tuning and the velocity of the airflow into the cylinder. The peak pressure (which we use to determine safe octane/timing) depends on how much air gets into the cylinder and compressed to TDC for combustion. Dynamic compression may tell you something at idle and low speed but when the engine is operating in it's power band it tells you very little. If Dynamic compression ratio relies on some of the air slipping back out of the intake valve because the valve is still open when the compression stroke starts. Cams with big duration and overlap would allow lots of air to slip out using this theory. The problem is that the air doesn't slip out. Instead it has developed momentum and is forced in even though the piston is rising. It's forced in through a combination of momentum and pressure waves in the intake and exhaust track. Indeed if a cam were to allow the air to slip out at high RPM the engine would not produce the power you want.

The required information for what you want is volumetric effieciency. Even with a very radical cam a well tuned engine can achieve a VE of 1.0 This means that even though the dynamic CR is low the cylinder pressure due to the factors above gets all the way up to what it would be assuming the static CR.

Yes race cams work better with High CR but you also need race gas if you have a well tuned engine for the cam.

Actually a good indication of VE is torque. If you look at the torque of a 2.2 or 2.4 T, E, or S engine you'll see that despite a lower Dynamic compression ratio the S an E have higher torque than the lower performance versions. This indicates that they have higher cylinder pressures not lower as you would assume from dynamic compression numbers.

Hope this makes sence to you.

-Andy"