Just buy a quantity and start upgrading your car, and if it runs out, it will tell you that the quantity has run out, so buy more :cros:
I have modification on my voteThere is already an existing F1 question telling you how many Engine Parts you beed to each level upgrade. But, still, someone might not know about it to make a search there. While the suggestion makes it directly visible and clear for whoever willing to tune his vehicle without the need to make that search into F1 panel.
I think creating a new field in the F1 menu that tells you how much the engine parts that each cars need to fully develop cost is better than your current suggestion. if yes iwill vote with :tick: