I’ve just bought the game, and it seems to me that the Fit Engine part of the Production line is a real bottleneck from the start.
A 4x4 supply area seems to need (per car):
1 flywheel (clutch?)
1 starter motor
1 (4?) brakes
1 steering column
1 steering wheel
While each ‘palette’ in the stockpile can store more than one component, the game seems to prioritise 12 PALETTES of valves, enough for 6 cars worth. So 62.5% of the stockpile space is useless at any one time until the valves are fitted. The game seems to use all 12 palettes, when it is time for the valves to be fitted,.