Production line is a great game. But, if you place 6 research centers at the beginning, you will complete all the researches and upgrades in 8 - 9 days.
If you play mainly in ultra speed it’s near 2-3 hours in real world. I think it’s too bad.
So perhaps, the solution is to reduct the speed of research center or really increase the required for each step.
If I have nothing to find it’s only product faster than other compagnies… bof. If I know that I need 16 - 20 hours to complete all researches it’s really more interesting.
I agree that research should be more costly. I think some of the car techs should require much more investment before getting them. There could also be technologies and labor training to make your overall operation more efficient or productive.