A theoretical analysis of the spark ignition VR/LE engine with the variable crank-radius to connecting-rod-length ratio R/L is presented. The studies have been performed with the help of the thermodynamic-type model (zero-dimensional) including NO formation submodel. The analysis have made it possible to determine the changes of some basic output engine parameters: thermal efficiency, work and NO concentration, as a result of the engine thermodynamic cycle variations which, in turn, result from the external regulation of the phase shift of the function R/L = f(φ), where φ is the crank angle. A comparison between the VR/LE and conventional engines is presented. The ranges of the phase angle which can give the gain in efficiency and NO emission reduction are also determined. The analysis has confirmed that the VR/LE engine concept has remarkable economy potential with application to the S1 engines and it is worth performing a research with an actual engine.