patricia heaton bikini It has to do with causing the piston to dwell longer at a higher pressure near TDC rather than letting it fall off into heat as quickly as forced by normal sinusoidal motion. The problem has been understood for a while and much more deeply than I do, but I can see how a cam profile can be selected to help a lot while a simple rotating crank pin doesn't give you very much freedom, though I think offset connecting rods are being used now for this reason.