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Old 01-18-2013, 11:25 AM
GunnerTHB GunnerTHB is offline
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There are several calculators out there that can calculate DCR for you. I've always heard target values of 8.5:1 for pump gas and 9:1 for race gas, although I'm sure that is pretty generalized and you could probably exceed that a little bit with good engine design.

Dynamic Compression is rooted in the fact that the intake valve closes after bottom dead center. Since your cylinder isn't sealed right away as the volume above the piston begins to decrease, you do not keep all of the air that is in the cylinder at BDC (Bottom Dead Center). What is compressed is what is left in the cylinder after the intake valve closes. This is why Dynamic Compression is always lower than Static Compression.

So one of the important things you need to know to calculate DCR is how long (in degrees of rotation) the intake valve stays open after the piston hits bottom dead center*.

When you are looking at your fuel you will have critical values, such as maximum pressure and temperature the fuel will take before autoignition, which is another thing to take into consideration when you get this intricate into engine design.

*Thanks to techinspector for teaching me how to do this several years ago.

Last edited by GunnerTHB; 01-18-2013 at 11:47 AM.
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