340 cam in a 318

No, you don't understand at all.
Knowing the Valve drop at TDC allows you to calculate what the valve drop would be at say 15 deg BTDC. Then if you know what the valve lift is at 15deg BTDC, then you have your answer.
You can then calculate for every degree of crank angle as long as you know the lift of the cam for that degree.
Pretty simple.