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Message: <blockquote data-quote="user 92" data-source="post: 80200" data-attributes="member: 92">My understanding of compression ratio is combustion chamber size - volume, compared to cylinder volume.Liquid is visible, so using liquid works for my imagination. Move the piston to btc and fill the cylinder volume with liquid. Lets say it took 10 parts to fill the volume. Move the piston to tdc and see how much came out. Lets say only 9 parts of the liquid came out, and left 1 part remaining.This is a 10:1 ratio. Reducing combustion chamber size will raise the compression ratio, like 10.5:1.Of course, higher compression ratio delivers higher pressure that needs to be dealt with.Several things can affect combustion chamber pressure in a running engine. Valve timing, ignition timing, throttle position, air/fuel ratio, quality of fuel, air density, and probably more that I can't think of right now. These things vary under varying conditions. Some vehicles now have Variable Valve Timing, but not our old wings.</blockquote>