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Although conventional CVS (Constant Volume Sampling) equipment is well established, future requirements for measuring the emitted concentrations of regulated components from ULEV (Ultra Low Emission Vehicles) cars will require optimized dilution ratios. By means of a needle driven by a stepper motor the variable CFV (Critical Flow Venturi)-CVS will be able to adjust the CVS maintaining critical conditions to a predefined volume in less than one second. Using this new design and operating it with software-controlled predefined volume modes, it will be possible to optimize dilution ratios by at least a factor of three. In this case ULEV measurements could be performed by using conventional analyzers.