The Dynamic Compression Ratio (DCR) is not to be confused with the Static Compression Ratio (SCR). The SCR is the compression ratio number that’s most often referred to when talking compression ratios but it is not the final say in determining if a particular engine is going to be pump gas friendly or not. While the SCR value may get you in the ball park, it is not accurate enough on those engine combinations that are built on the ragged edge for pump gasoline use versus needing a blend of higher octane fuel and/or racing fuel. The SCR value is simply the calculation that is the result of the difference in values of the piston being at bottom dead center versus the piston being at top dead center. Camshaft events and piston connecting rod lengths do not play a part in the SCR calculation which is where the DCR comes into play.
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Cylinder Head Testing – Part 1
What was originally planned as a simple cylinder head test on the 312 dyno mule ended up being a test that ultimately involved over two dozen different sets of cylinder heads. While part of this testing was a precursor to determining which pair of heads were to be used for an extensive exhaust system test, the remainder of the cylinder head test was to answer some questions about the significance of milling and porting on some of the various heads. This test saw no fewer than thirty different head changes on the engine as some of those pairs of heads were reworked differently between the tests or were reinstalled as part of the base-lining that was being performed to insure that the engine performance was remaining constant.
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