A classic production line for mixed models with a fixed cycle time is transformed into a flowshop by removing the time restrictions at the workstations. In the new production line, the Heijunka concept of Just in Time manufacturing is applied, imposing on the sequences of products that they preserve the production mix through linear constraints. In this work, we propose a MILP model for the new problem which is solved with the IBM-CPLEX solver using the set of 23 Nissan-9Eng.I instances. It is concluded that the economic impact due to production losses is very significant when the buffers between the stations of the engine production line are suppressed (1224 €/day), while the economic impact generated by Heijunka is negligible (9.83 €/day) compared to the economic and management advantages it offers.