AFIK, there is no way to easily reference engine wash..you'd have to make a variable for EACH engines wash...
Maby proportional engine damage/speed can be a SCP flag? Or mission flag?
You don't get my point. Engine wash values should be considered as a reference.
For example:
Max speed of a ship is 50. There are two big engine thrusters and two little ones. I say that each big engine increases the speed by 20 and every small engine increases the speed by 5.
But, when I check engine wash values, I realize that my system was wrong. I modify it in order to make it fill its role better(+15 for each big engine, +10 for each small engine).