The Tour split-cycle engine implements a superior thermal management strategy that reduces the magnitude of the two major thermal losses in conventional 4-stroke engines - heat loss to coolant/oil and exhaust energy or enthalpy loss.
The heat rejected to the cylinder walls (and absorbed by the coolant/oil) is, to first order, proportional to the temperature difference between the bulk gas temperature and the average wall temperature, where most of the heat is rejected during the expansion and exhaust part of the cycle since the temperature difference by far outweighs the temperature difference during the induction and compression part of the cycle. Since any split-cycle approach, including the Tour cycle approach, separates and assigns the cold and hot portions of the full thermodynamic cycle to separate cylinders, it is now possible to control their respective wall temperatures in order to lower the temperature differences of both the induction/compression and combustion/exhaust strokes. In particular, raising the wall temperature of the Hot-Cylinder noticeably decreases the temperature difference during the combustion/exhaust strokes. Obviously, the wall temperature of the Hot-Cylinder can only be raised within reason to safeguard the proper functioning of the piston ring lubrication and maintaining engine reliability.