Car Ramming Damage System

I am having a problem with a car game I am currently developing. I am trying to make a damage system which takes into account mass and velocity however when I do I have problems with the car hitting the other taking more damage.

I want it so that the system takes into account whoever is ramming into the other player and gives more damage. The direction of the velocity also as if the cars are side to side and ram, it takes into the equation the large velocity and takes a lot of health off.

Any help would be appreciated.